fix(ci): SHA-pin codecov-action for consistency

Author: zfarrell

.github/workflows/ci.yml

@@ -33,7 +33,7 @@ jobs:
         run: cargo llvm-cov --lcov --output-path lcov.info
 
       - name: Upload coverage to Codecov
-        uses: codecov/codecov-action@v5
+        uses: codecov/codecov-action@75cd11691c0faa626561e295848008c8a7dddffe # v5
         with:
           files: lcov.info
           fail_ci_if_error: false