build(deps): bump actions/checkout from 2.4.0 to 3

Bumps [actions/checkout](https://github.com/actions/checkout) from 2.4.0 to 3.
- [Release notes](https://github.com/actions/checkout/releases)
- [Changelog](https://github.com/actions/checkout/blob/main/CHANGELOG.md)
- [Commits](actions/checkout@ec3a7ce...a12a394)

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

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

Author: dependabot[bot]

.github/workflows/ci.yml

@@ -41,7 +41,7 @@ jobs:
 
     steps:
       - name: Checkout TUF
-        uses: actions/checkout@ec3a7ce113134d7a93b817d10a8272cb61118579
+        uses: actions/checkout@a12a3943b4bdde767164f792f33f40b04645d846
 
       - name: Set up Python ${{ matrix.python-version }}
         uses: actions/setup-python@0ebf233433c08fb9061af664d501c3f3ff0e9e20

.github/workflows/specification-version.yml

@@ -14,7 +14,7 @@ jobs:
     name: Open an issue when spec version bumps
     runs-on: ubuntu-latest
     steps:
-    - uses: actions/checkout@ec3a7ce113134d7a93b817d10a8272cb61118579
+    - uses: actions/checkout@a12a3943b4bdde767164f792f33f40b04645d846
     - uses: actions/setup-python@0ebf233433c08fb9061af664d501c3f3ff0e9e20
     - name: Get supported version
       id: get-version