message: Fix a compiler warning in ModuleCacheTest.cpp, NFC
diff: @@ -102,7 +102,7 @@ void ModuleCacheTest::TryGetAndPut(const FileSpec &cache_dir,
  Status error = mc.GetAndPut(
  cache_dir, hostname, module_spec,
  - [this, &download_called](const ModuleSpec &module_spec,
  + [&download_called](const ModuleSpec &module_spec,
  const FileSpec &tmp_download_file_spec) {
  download_called = true;
  EXPECT_STREQ(GetDummyRemotePath().GetCString(),
  