Bump cortex-m in /rtic_v1/stm32f4_independent_watchdog

Bumps [cortex-m](https://github.com/rust-embedded/cortex-m) from 0.7.6 to 0.7.7.
- [Release notes](https://github.com/rust-embedded/cortex-m/releases)
- [Changelog](https://github.com/rust-embedded/cortex-m/blob/v0.7.7/CHANGELOG.md)
- [Commits](rust-embedded/cortex-m@v0.7.6...v0.7.7)

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

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Author: dependabot[bot]