[GHA] Fix Dockerfile change detection

Author: Quasar6X

.github/workflows/build.yaml

@@ -27,12 +27,14 @@ jobs:
 
     steps:
       - name: Checkout
-        uses: actions/checkout@v4
+        uses: actions/checkout@v6
+        with:
+          fetch-depth: 2
 
       - name: Check for Docker changes
         id: changes
         run: |
-          if git diff --name-only ${{ github.event.before }} ${{ github.sha }} | grep '^\.devcontainer/Dockerfile'; then
+          if git diff --name-only HEAD~1 HEAD | grep '^\.devcontainer/Dockerfile'; then
             echo "changed=true" >> $GITHUB_OUTPUT
           else
             echo "changed=false" >> $GITHUB_OUTPUT
@@ -86,7 +88,7 @@ jobs:
 
     steps:
       - name: Checkout
-        uses: actions/checkout@v4
+        uses: actions/checkout@v6
 
       - name: Run latexmk
         run: |