chore: add GCF buildpack integration test Workflow

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

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

@@ -0,0 +1,19 @@
+# Validates Functions Framework with GCF buildpacks.
+name: Buildpack Integration Test
+on:
+  push:
+    branches:
+      - main
+  workflow_dispatch:
+jobs:
+  ruby30-buildpack-test:
+    uses: GoogleCloudPlatform/functions-framework-conformance/.github/workflows/[email protected]
+    with:
+      http-builder-source: 'test/conformance'
+      http-builder-target: 'http_func'
+      cloudevent-builder-source: 'test/conformance'
+      cloudevent-builder-target: 'cloudevent_func'
+      prerun: 'test/conformance/prerun.sh ${{ github.sha }}'
+      builder-runtime: 'ruby30'
+      # Latest uploaded tag from us.gcr.io/fn-img/buildpacks/ruby30/builder
+      builder-tag: 'ruby30_20220620_3_0_4_RC00'

test/conformance/.gitignore

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+# These files are generate dynamically based off the git commit sha
+# when trying to build the conformance test function with buildpacks,
+# and should not be checked in.
+Gemfile
+Gemfile.lock

test/conformance/prerun.sh

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+# prerun.sh sets up the test function to use the functions framework commit
+# specified. This makes the function `pack` buildable with GCF buildpacks.
+#
+# `pack` build example command:
+# pack build myfn --verbose --builder us.gcr.io/fn-img/buildpacks/ruby30/builder:ruby30_20220620_3_0_4_RC00 --env GOOGLE_RUNTIME=ruby30 --env GOOGLE_FUNCTION_TARGET=http_func --env X_GOOGLE_TARGET_PLATFORM=gcf
+FRAMEWORK_VERSION=$1
+
+# exit when any command fails
+set -e
+
+cd $(dirname $0)
+
+if [ -z "${FRAMEWORK_VERSION}" ]
+    then
+        echo "Functions Framework version required as first parameter"
+        exit 1
+fi
+
+echo "source 'https://rubygems.org'
+gem 'functions_framework', github: 'GoogleCloudPlatform/functions-framework-ruby', ref: '$FRAMEWORK_VERSION'" > Gemfile
+cat Gemfile
+
+sudo gem install bundler
+
+# Generate a Gemfile.lock without installing any Gems
+bundle lock --update
+cat Gemfile.lock