.github/: skip file conflicts check if no packages are built

workflow was limited to branches modifying srcpkgs/, but this
still triggered when modifying only update files or removing template

.github/workflows/build.yaml

@@ -105,8 +105,10 @@ jobs:
       - name: Check file conflicts
         if: matrix.config.arch == 'x86_64' # the arch indexed in xlocate
         run: |
-          xlocate -S &&
-          common/scripts/lint-conflicts $HOME/hostdir/binpkgs
+          if [ -s /tmp/templates ]; then
+              xlocate -S &&
+              common/scripts/lint-conflicts $HOME/hostdir/binpkgs
+          fi
 
       - name: Verify repository state
         run: |