Bump libsecp256k1 from 0.6.0 to 0.7.0 (#10214)

* Bump libsecp256k1 from 0.6.0 to 0.7.0

Bumps [libsecp256k1](https://github.com/paritytech/libsecp256k1) from 0.6.0 to 0.7.0.
- [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-minor
...

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

* Fix pallet_contracts for new libsecp256k1 version

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