Bump symfony/stopwatch from 3.4.0 to 3.4.21

Bumps [symfony/stopwatch](https://github.com/symfony/stopwatch) from 3.4.0 to 3.4.21.
- [Release notes](https://github.com/symfony/stopwatch/releases)
- [Changelog](https://github.com/symfony/stopwatch/blob/master/CHANGELOG.md)
- [Commits](symfony/stopwatch@v3.4.0...v3.4.21)

Signed-off-by: dependabot[bot] <support@dependabot.com>

Author: dependabot-support