Fix file mtime test

crates/ruff_cli/src/cache.rs

@@ -509,17 +509,22 @@ mod tests {
         test_cache.write_source_file("source.py", source);
         assert_eq!(cache.new_files.lock().unwrap().len(), 0);
 
-        let expected_diagnostics = test_cache
+        test_cache
             .lint_file_with_cache("source.py", &cache)
             .expect("Failed to lint test file");
 
         cache.store().unwrap();
         let cache = test_cache.open();
 
-        // Write the same contents to the source file (updating the modified time)
-        test_cache.write_source_file("source.py", source);
+        // Write new contents to the source file (updating the modified time)
+        // Note we cannot just write the same content because some file systems will not perform the write
+        // Once https://doc.rust-lang.org/std/fs/struct.File.html#method.set_modified is stable we can
+        // just update the modified time without appending content which will allow us to assert that
+        // the diagnostics have not changed.
+        let new_content: &[u8] = b"# new content\n";
+        test_cache.write_source_file("source.py", &[source, new_content].concat());
 
-        let got_diagnostics = test_cache
+        test_cache
             .lint_file_with_cache("source.py", &cache)
             .expect("Failed to lint test file");
 
@@ -528,11 +533,6 @@ mod tests {
             1,
             "Cache should not be used, the file should be treated as new and added to the cache"
         );
-
-        assert!(
-            expected_diagnostics == got_diagnostics,
-            "The diagnostics should not change"
-        );
     }
 
     #[test]