Simplify taging logic to avoid repetition

Author: ljmnoonan

.github/workflows/ci.yaml

@@ -47,10 +47,10 @@ jobs:
     env:
       # Indicates what's the equivalent to tecnativa/postgres-autoconf:latest image
       LATEST_RELEASE: "18-alpine"
-      DOCKER_TAG: ${{ matrix.pg_version }}-alpine
+      BASE_TAG: ${{ matrix.pg_version }}-alpine
+      DOCKER_TAG: ${{ github.event_name == 'pull_request' && format('{0}-test-pr{1}', matrix.pg_version, github.event.number) || format('{0}-alpine', matrix.pg_version) }}
       GIT_SHA1: ${{ github.sha }}
       PG_VERSION: ${{ matrix.pg_version }}
-      IS_PR: ${{ github.event_name == 'pull_request' }}
       PUBLISH: ${{ github.ref == 'refs/heads/master' || (github.event_name == 'pull_request' && github.event.pull_request.head.repo.full_name == github.repository) }}
       # Github does not allow evaluating a secret in an if condition, so we need to set them as environment variables
       DOCKERHUB_TOKEN: ${{ secrets.DOCKERHUB_TOKEN }}
@@ -72,16 +72,6 @@ jobs:
       - run: ./hooks/build
       # Test
       - run: python -m unittest tests.test -v
-      - name: Set Docker Tag
-        run: |
-          if [ "${{ env.IS_PR }}" = "true" ]; then
-            echo "DOCKER_TAG=${{ matrix.pg_version }}-test-pr${{ github.event.number }}" >> $GITHUB_ENV
-          else
-            echo "DOCKER_TAG=${{ matrix.pg_version }}-alpine" >> $GITHUB_ENV
-          fi
-      - name: Tag Docker Image for PR
-        if: env.IS_PR
-        run: docker tag ${{ env.DOCKER_REPO }}:${{ matrix.pg_version }}-alpine ${{ env.DOCKER_REPO }}:${{ env.DOCKER_TAG }}
       - name: Set up QEMU
         if: env.PUBLISH
         uses: docker/setup-qemu-action@v4

hooks/build

@@ -3,6 +3,7 @@ from plumbum import FG, local
 from plumbum.cmd import date, docker
 
 # Check environment variables are present
+BASE_TAG = local.env["BASE_TAG"]
 DOCKER_TAG = local.env["DOCKER_TAG"]
 REPO = local.env["DOCKER_REPO"]
 COMMIT = local.env.get("GIT_SHA1")
@@ -18,7 +19,7 @@ DATE = date("--rfc-3339", "ns")
         "--build-arg",
         "BUILD_DATE={}".format(DATE),
         "--build-arg",
-        "BASE_TAG={}".format(DOCKER_TAG),
+        "BASE_TAG={}".format(BASE_TAG),
         "--tag",
         "{}:{}".format(REPO, DOCKER_TAG),
         ".",