.github: check file conflicts in x86_64 build job

.github/workflows/build.yaml

@@ -94,6 +94,12 @@ jobs:
           "$here/common/travis/show_files.sh" "$BOOTSTRAP" "$ARCH"
           )
 
+      - 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
+
       - name: Verify repository state
         run: |
           (