Bump libsecp256k1 from 0.7.0 to 0.7.1 (paritytech#773)

Bumps [libsecp256k1](https://github.com/paritytech/libsecp256k1) from 0.7.0 to 0.7.1.
- [Release notes](https://github.com/paritytech/libsecp256k1/releases)
- [Changelog](https://github.com/paritytech/libsecp256k1/blob/master/CHANGELOG.md)
- [Commits](https://github.com/paritytech/libsecp256k1/commits)

---
updated-dependencies:
- dependency-name: libsecp256k1
  dependency-type: direct:production
  update-type: version-update:semver-patch
...

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

Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>