ci: fix GitHub Action

It look like the variable may be uninitialized

    ...sh: line 11: [: -ne: unary operator expected
    ...sh: line 11: [: -ne: unary operator expected
    Lockfile ./Cargo.lock is dirty
    Error: Process completed with exit code 1.

Signed-off-by: Pablo Barbáchano <[email protected]>

Author: pb8o

.github/workflows/deny_dirty_cargo_locks.yml

@@ -11,16 +11,17 @@ jobs:
         with:
           ref: ${{ github.event.pull_request.head.sha }}
 
-      - name: "Check no Cargo.lock files are dirty" 
+      - name: "Check no Cargo.lock files are dirty"
         run: |
           exit_code=0
+          is_dirty=0
           # This breaks for paths with whitespaces in them, but we have an integration test
           # that prevents those from existing in this repository.
           for f in $(find . -name 'Cargo.lock' -not -path "./build/*"); do
             (
               cd "$(dirname "$f")"
               cargo --locked metadata --format-version 1 >/dev/null 2>&1
-            ) || is_dirty=$?;  
+            ) || is_dirty=$?;
             # GitHub Actions execute run steps as `bash -e`, so we need the temporary
             # variable to not exit early.
             if [ $is_dirty -ne 0 ]; then