Fix a race in file I/O done by a BuildRunner test (#54167)

jason-simmons · web-flow · commit f0effaaf4001 · 2024-07-28T00:57:26.000Z
This test failure had been seen in some recent auto-roller jobs on CI.
diff --git a/tools/pkg/engine_build_configs/test/build_config_runner_test.dart b/tools/pkg/engine_build_configs/test/build_config_runner_test.dart
@@ -834,7 +834,7 @@ void main() {
             ..createSync(recursive: true);
       final io.File file =
           io.File(path.join(hostDebug.path, 'compile_commands.json'));
-      file.writeAsString(
+      file.writeAsStringSync(
         r'''
 [
   {

Original file line number	Diff line number	Diff line change
`@@ -834,7 +834,7 @@ void main() {`
`834`	`834`	`..createSync(recursive: true);`
`835`	`835`	`final io.File file =`
`836`	`836`	`io.File(path.join(hostDebug.path, 'compile_commands.json'));`
`837`		`- file.writeAsString(`
	`837`	`+ file.writeAsStringSync(`
`838`	`838`	`r'''`
`839`	`839`	`[`
`840`	`840`	`{`