Bump actions/checkout from 2 to 3 (#150)

Bumps [actions/checkout](https://github.com/actions/checkout) from 2 to 3.
- [Release notes](https://github.com/actions/checkout/releases)
- [Changelog](https://github.com/actions/checkout/blob/main/CHANGELOG.md)
- [Commits](actions/checkout@v2...v3)

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

[skip ci]

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

.github/workflows/CompatHelper.yml

@@ -9,7 +9,7 @@ jobs:
   CompatHelper:
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v2
+      - uses: actions/checkout@v3
       - name: Get Julia compatibility
         id: julia_compat
         # NOTE: this requires a Julia compat lower-bound with minor version!

.github/workflows/ManifestUpdater.yml

@@ -9,7 +9,7 @@ jobs:
   ManifestUpdater:
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v2
+      - uses: actions/checkout@v3
       - name: Get Julia compatibility
         id: julia_compat
         # NOTE: this requires a Julia compat lower-bound with minor version!