CI(check-build-tools-image): change build-tools image persistent tag (#8059)

## Problem

We don't rebuild `build-tools` image for changes in a workflow that
builds this image itself
(`.github/workflows/build-build-tools-image.yml`) or in a workflow that
determines which tag to use
(`.github/workflows/check-build-tools-image.yml`)

## Summary of changes
- Use a hash of `Dockerfile.build-tools` and workflow files as a
persistent tag instead of using a commit sha.

.github/workflows/build-build-tools-image.yml

@@ -30,7 +30,6 @@ jobs:
   check-image:
     uses: ./.github/workflows/check-build-tools-image.yml
 
-  # This job uses older version of GitHub Actions because it's run on gen2 runners, which don't support node 20 (for newer versions)
   build-image:
     needs: [ check-image ]
     if: needs.check-image.outputs.found == 'false'

.github/workflows/check-build-tools-image.yml

@@ -25,26 +25,17 @@ jobs:
       found: ${{ steps.check-image.outputs.found }}
 
     steps:
+      - uses: actions/checkout@v4
+
       - name: Get build-tools image tag for the current commit
         id: get-build-tools-tag
         env:
-          # Usually, for COMMIT_SHA, we use `github.event.pull_request.head.sha || github.sha`, but here, even for PRs,
-          # we want to use `github.sha` i.e. point to a phantom merge commit to determine the image tag correctly.
-          COMMIT_SHA: ${{ github.sha }}
-          GH_TOKEN: ${{ secrets.GITHUB_TOKEN }}
+          IMAGE_TAG: |
+            ${{ hashFiles('Dockerfile.build-tools',
+                          '.github/workflows/check-build-tools-image.yml',
+                          '.github/workflows/build-build-tools-image.yml') }}
         run: |
-          LAST_BUILD_TOOLS_SHA=$(
-            gh api \
-              -H "Accept: application/vnd.github+json" \
-              -H "X-GitHub-Api-Version: 2022-11-28" \
-              --method GET \
-              --field path=Dockerfile.build-tools \
-              --field sha=${COMMIT_SHA} \
-              --field per_page=1 \
-              --jq ".[0].sha" \
-              "/repos/${GITHUB_REPOSITORY}/commits"
-          )
-          echo "image-tag=${LAST_BUILD_TOOLS_SHA}" | tee -a $GITHUB_OUTPUT
+          echo "image-tag=${IMAGE_TAG}" | tee -a $GITHUB_OUTPUT
 
       - name: Check if such tag found in the registry
         id: check-image