chore: add GCF buildpack integration test Workflow

See [functions-framework-conformance builidpack integration workflow PR](GoogleCloudPlatform/functions-framework-conformance#99) for more information.

Also, move the script for running conformance tests locally to the
conformance test directory.

.github/workflows/buildpack-integration-test.yml

@@ -16,4 +16,15 @@ jobs:
       prerun: 'tests/conformance/prerun.sh ${{ github.sha }}'
       builder-runtime: 'php74'
       # Latest uploaded tag from us.gcr.io/fn-img/buildpacks/php74/builder
-      builder-tag: 'php74_20220620_7_4_29_RC00'
+      builder-tag: 'php74_20220620_7_4_29_RC00'
+  php81-buildpack-test:
+    uses: GoogleCloudPlatform/functions-framework-conformance/.github/workflows/[email protected]
+    with:
+      http-builder-source: 'tests/conformance'
+      http-builder-target: 'declarativeHttpFunc'
+      cloudevent-builder-source: 'tests/conformance'
+      cloudevent-builder-target: 'declarativeCloudEvent'
+      prerun: 'tests/conformance/prerun.sh ${{ github.sha }}'
+      builder-runtime: 'php81'
+      # Latest uploaded tag from us.gcr.io/fn-img/buildpacks/php81/builder
+      builder-tag: 'php81_20220620_8_1_6_RC00'