Bump psalm/plugin-symfony from 3.1.5 to 3.1.6 in /tools/psalm

Bumps [psalm/plugin-symfony](https://github.com/psalm/psalm-plugin-symfony) from 3.1.5 to 3.1.6.
- [Release notes](https://github.com/psalm/psalm-plugin-symfony/releases)
- [Commits](psalm/psalm-plugin-symfony@v3.1.5...v3.1.6)

---
updated-dependencies:
- dependency-name: psalm/plugin-symfony
  dependency-type: direct:development
  update-type: version-update:semver-patch
...

Signed-off-by: dependabot[bot] <[email protected]>