[ci] fix subsystem-benchmarks gha (#3876)

PR adds variables validation and app credentials for pushing into
gh-pages

cc https://github.com/paritytech/ci_cd/issues/934

.github/workflows/subsystem-benchmarks.yml

@@ -15,7 +15,13 @@ on:
 jobs:
   subsystem-benchmarks:
     runs-on: ubuntu-latest
+    environment: subsystem-benchmarks
     steps:
+      - name: Validate inputs
+        run: |
+          echo "${{ github.event.inputs.benchmark-data-dir-path }}" | grep -P '^[a-z\-]'
+          echo "${{ github.event.inputs.output-file-path }}" | grep -P '^[a-z\-]+\.json'
+
       - name: Checkout Sources
         uses: actions/checkout@v4.1.2
         with:
@@ -30,7 +36,13 @@ jobs:
       - name: Switch branch
         id: step_two
         run: |
-          git checkout master
+          git checkout master --
+
+      - uses: actions/create-github-app-token@v1
+        id: app-token
+        with:
+          app-id: ${{ secrets.POLKADOTSDK_GHPAGES_APP_ID }}
+          private-key: ${{ secrets.POLKADOTSDK_GHPAGES_APP_KEY }}
 
       - name: Store benchmark result
         uses: benchmark-action/github-action-benchmark@v1
@@ -38,5 +50,5 @@ jobs:
           tool: "customSmallerIsBetter"
           output-file-path: ${{ github.event.inputs.output-file-path }}
           benchmark-data-dir-path: "bench/${{ github.event.inputs.benchmark-data-dir-path }}"
-          github-token: ${{ secrets.GITHUB_TOKEN }}
+          github-token: ${{ steps.app-token.outputs.token }}
           auto-push: true