Improve the inline docs around matrix exclusions

.github/workflows/install-testing.yml

@@ -78,15 +78,17 @@ jobs:
 
         # Exclude some PHP and MySQL versions that cannot currently be tested with Docker containers.
         exclude:
+          # There are no local WordPress Docker environment containers for PHP <= 5.3.
           - php: '5.2'
           - php: '5.3'
+          # MySQL containers <= 5.5 do not exist or fail to start properly.
           - db-version: '5.0'
+            db-type: 'mysql'
           - db-version: '5.1'
+            db-type: 'mysql'
           - db-version: '5.5'
-          - php: '7.2'
-            db-version: '8.4'
-          - php: '7.3'
-            db-version: '8.4'
+            db-type: 'mysql'
+          # MySQL 9.0+ will not work on PHP 7.2 & 7.3. See https://core.trac.wordpress.org/ticket/61218.
           - php: '7.2'
             db-version: '9.0'
           - php: '7.3'
@@ -97,6 +99,8 @@ jobs:
         image: ${{ matrix.db-type }}:${{ matrix.db-version }}
         ports:
           - 3306
+        volumes:
+          - ${{ contains( fromJSON('["7.2", "7.3"]'), matrix.php ) && './tools/local-env/mysql-old-php.conf:/etc/mysql/conf.d/config-file.cnf' || './tools/local-env/mysql-init.sql:/docker-entrypoint-initdb.d/mysql-init.sql' }}
         options: >-
           --health-cmd="mysqladmin ping"
           --health-interval="30s"
@@ -105,7 +109,7 @@ jobs:
           -e MYSQL_ROOT_PASSWORD="root"
           -e MYSQL_DATABASE="test_db"
           --entrypoint sh ${{ matrix.db-type }}:${{ matrix.db-version }}
-          -c "exec docker-entrypoint.sh mysqld${{ matrix.db-type == 'mysql' && contains( fromJSON('["7.2", "7.3"]'), matrix.php ) && ' --default-authentication-plugin=mysql_native_password' || '' }}"
+          -c "exec docker-entrypoint.sh mysqld${{ contains( fromJSON('["7.2", "7.3"]'), matrix.php ) && '8.4' == matrix.db-version && ' --authentication-policy=mysql_native_password' || contains( fromJSON('["7.2", "7.3"]'), matrix.php ) && ' --default-authentication-plugin=mysql_native_password' || '' }}"
 
     steps:
       - name: Set up PHP ${{ matrix.php }}

.github/workflows/phpunit-tests.yml

@@ -93,7 +93,7 @@ jobs:
             report: true
 
         exclude:
-          # MySQL 9.0+ will not work on PHP 7.2 & 7.3
+          # MySQL 9.0+ will not work on PHP 7.2 & 7.3. See https://core.trac.wordpress.org/ticket/61218.
           - php: '7.2'
             db-version: '9.0'
           - php: '7.3'

.github/workflows/reusable-upgrade-testing.yml

@@ -57,6 +57,8 @@ jobs:
         image: ${{ inputs.db-type }}:${{ inputs.db-version }}
         ports:
           - 3306
+        volumes:
+          - ${{ contains( fromJSON('["7.2", "7.3"]'), matrix.php ) && './tools/local-env/mysql-old-php.conf:/etc/mysql/conf.d/config-file.cnf' || './tools/local-env/mysql-init.sql:/docker-entrypoint-initdb.d/mysql-init.sql' }}
         options: >-
           --health-cmd="mysqladmin ping"
           --health-interval="30s"
@@ -65,7 +67,7 @@ jobs:
           -e MYSQL_ROOT_PASSWORD="root"
           -e MYSQL_DATABASE="test_db"
           --entrypoint sh ${{ inputs.db-type }}:${{ inputs.db-version }}
-          -c "exec docker-entrypoint.sh mysqld${{ inputs.db-type == 'mysql' && contains( fromJSON('["7.2", "7.3"]'), inputs.php ) && ' --default-authentication-plugin=mysql_native_password' || '' }}"
+          -c "exec docker-entrypoint.sh mysqld${{ contains( fromJSON('["7.2", "7.3"]'), matrix.php ) && '8.4' == matrix.db-version && ' --authentication-policy=mysql_native_password' || contains( fromJSON('["7.2", "7.3"]'), matrix.php ) && ' --default-authentication-plugin=mysql_native_password' || '' }}"
 
     steps:
       - name: Set up PHP ${{ inputs.php }}

.github/workflows/upgrade-testing.yml

@@ -75,11 +75,6 @@ jobs:
         wp: [ '6.0', '6.1', '6.2', '6.3', '6.4', '6.5', '6.6', '6.7' ]
         multisite: [ false, true ]
 
-        exclude:
-          - php: '7.2'
-            db-version: '8.4'
-          - php: '7.3'
-            db-version: '8.4'
     with:
       os: ${{ matrix.os }}
       php: ${{ matrix.php }}
@@ -104,11 +99,6 @@ jobs:
         wp: [ '5.0', '5.1', '5.2', '5.3', '5.4', '5.5', '5.6', '5.7', '5.8', '5.9' ]
         multisite: [ false, true ]
 
-        exclude:
-          - php: '7.2'
-            db-version: '8.4'
-          - php: '7.3'
-            db-version: '8.4'
     with:
       os: ${{ matrix.os }}
       php: ${{ matrix.php }}
@@ -160,11 +150,6 @@ jobs:
         wp: [ '4.1', '4.2', '4.3', '4.4', '4.5', '4.6', '4.7', '4.8', '4.9' ]
         multisite: [ false, true ]
 
-        exclude:
-          - php: '7.2'
-            db-version: '8.4'
-          - php: '7.3'
-            db-version: '8.4'
     with:
       os: ${{ matrix.os }}
       php: ${{ matrix.php }}

tools/local-env/old-php-mysql-84.override.yml

@@ -3,3 +3,8 @@ services:
   mysql:
     volumes:
       - ./tools/local-env/mysql-old-php.conf:/etc/mysql/conf.d/config-file.cnf
+
+  # This is currently only used in the upgrade and installation test GitHub Action workflows.
+  database:
+    volumes:
+      - ./tools/local-env/mysql-old-php.conf:/etc/mysql/conf.d/config-file.cnf