Bump build_runner from 2.4.6 to 2.4.7

Bumps [build_runner](https://github.com/dart-lang/build) from 2.4.6 to 2.4.7.
- [Release notes](https://github.com/dart-lang/build/releases)
- [Commits](dart-lang/build@build_runner-v2.4.6...build_runner-v2.4.7)

---
updated-dependencies:
- dependency-name: build_runner
  dependency-type: direct:production
  update-type: version-update:semver-patch
...

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