Bump actions/checkout from 4.1.7 to 4.2.1

Bumps [actions/checkout](https://github.com/actions/checkout) from 4.1.7 to 4.2.1.
- [Release notes](https://github.com/actions/checkout/releases)
- [Changelog](https://github.com/actions/checkout/blob/main/CHANGELOG.md)
- [Commits](https://github.com/actions/checkout/compare/v4.1.7...v4.2.1)

---
updated-dependencies:
- dependency-name: actions/checkout
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

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

.github/workflows/coverage.yaml

@@ -17,7 +17,7 @@ jobs:
     runs-on: ubuntu-latest
 
     steps:
-      - uses: actions/checkout@v4.1.7
+      - uses: actions/checkout@v4.2.1
         with:
           persist-credentials: false
 

.github/workflows/main.yml

@@ -7,7 +7,7 @@ jobs:
     name: build on MSRV
     runs-on: ubuntu-latest
     steps:
-    - uses: actions/checkout@v4.1.7
+    - uses: actions/checkout@v4.2.1
     - uses: dtolnay/rust-toolchain@1.65.0
     # Don't use --all-features because `frost` has a higher MSRV and it's non-default.
     # Also don't run tests because some dev-dependencies have higher MSRVs.
@@ -16,7 +16,7 @@ jobs:
     name: test on nightly
     runs-on: ubuntu-latest
     steps:
-    - uses: actions/checkout@v4.1.7
+    - uses: actions/checkout@v4.2.1
     - uses: dtolnay/rust-toolchain@nightly
     # Update dependencies since we commit the lockfile
     - run: cargo update --verbose
@@ -25,7 +25,7 @@ jobs:
     name: build with no_std
     runs-on: ubuntu-latest
     steps:
-    - uses: actions/checkout@v4.1.7
+    - uses: actions/checkout@v4.2.1
     - uses: dtolnay/rust-toolchain@master
       with:
         toolchain: stable