ci(actions): upgrade to Ubuntu 24.04 and Python 3.12 (reanahub#11)

Closes reanahub/reana#808

.github/workflows/ci.yml

@@ -10,7 +10,7 @@ on: [push, pull_request]
 
 jobs:
   lint-commitlint:
-    runs-on: ubuntu-20.04
+    runs-on: ubuntu-24.04
     steps:
       - name: Checkout
         uses: actions/checkout@v4
@@ -36,7 +36,7 @@ jobs:
           ./run-tests.sh --check-commitlint ${{ github.event.pull_request.head.sha }}~${{ github.event.pull_request.commits }} ${{ github.event.pull_request.head.sha }} ${{ github.event.pull_request.number }}
 
   lint-shellcheck:
-    runs-on: ubuntu-20.04
+    runs-on: ubuntu-24.04
     steps:
       - name: Checkout
         uses: actions/checkout@v4

README.md

@@ -21,7 +21,7 @@ For example, to validate the `reana.yaml` file of a demo example, you can add th
 
 ```yaml
 validate:
-  runs-on: ubuntu-20.04
+  runs-on: ubuntu-24.04
   steps:
     - name: Checkout
       uses: actions/checkout@v3

local-run/action.yml

@@ -10,7 +10,7 @@ runs:
     - name: Setup Python
       uses: actions/setup-python@v5
       with:
-        python-version: 3.8
+        python-version: 3.12
 
     - name: Install Python dependencies
       run: |

local-validate/action.yml

@@ -13,7 +13,7 @@ runs:
     - name: Setup Python
       uses: actions/setup-python@v5
       with:
-        python-version: 3.8
+        python-version: 3.12
 
     - name: Install Python dependencies
       run: |

release-docker/action.yml

@@ -44,7 +44,7 @@ runs:
     - name: Setup Python
       uses: actions/setup-python@v5
       with:
-        python-version: 3.8
+        python-version: 3.12
 
     - name: Install Python dependencies
       run: |