Use commit hash instead of mutable tag

Author: matthewelwell

.github/workflows/api-fix-docs-artefacts.yml

@@ -28,7 +28,7 @@ jobs:
     steps:
       - name: Generate GitHub App token with push access
         id: app-token
-        uses: actions/create-github-app-token@v3
+        uses: actions/create-github-app-token@bcd2ba49218906704ab6c1aa796996da409d3eb1
         with:
           client-id: ${{ vars.FLAGSMITH_ENGINEERING_GH_APP_ID }}
           private-key: ${{ secrets.FLAGSMITH_ENGINEERING_GH_APP_PRIVATE_KEY }}