Use fixed alpine version

Not specifying alpine version causes libssl version
to change, which in turn cause error in downgrade tests
as well as ABI tests

.github/workflows/abi.yaml

@@ -89,7 +89,9 @@ jobs:
 
     - name: Run tests
       run: |
-        TEST_IMAGE="postgres:${{ matrix.tester }}-alpine"
+        # We need to use same libssl version used in the latest official TimescaleDB container images.
+        # So we will use the fixed alpine version, this will guarantee that libssl version wont change.
+        TEST_IMAGE="postgres:${{ matrix.tester }}-alpine-3.16"
 
         docker run -i --rm -v $(pwd):/mnt ${TEST_IMAGE} bash <<"EOF"
           apk add cmake gcc make build-base krb5-dev openssl-dev sudo > /dev/null

.github/workflows/update-test.yaml

@@ -79,7 +79,9 @@ jobs:
         PG_MAJOR=$(echo "${{ matrix.pg }}" | sed -e 's![.].*!!')
         UPDATE_FROM_TAG=${DOWNGRADE_TO}-pg${PG_MAJOR}
         export UPDATE_FROM_TAG
-        scripts/test_downgrade_from_tag.sh
+        # We need to use same libssl version used in the latest official TimescaleDB container images.
+        # So we will use the fixed alpine version, this will guarantee that libssl version wont change.
+        PG_IMAGE_TAG="${PG_VERSION}-alpine3.16" scripts/test_downgrade_from_tag.sh
 
     - name: Downgrade diff
       if: failure()