Bump actions/checkout from 2.4.0 to 3 (flutter#50)

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] <[email protected]>

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

Author: dependabot[bot]

impeller/.github/workflows/scorecards-analysis.yml

@@ -20,7 +20,7 @@ jobs:
 
     steps:
       - name: "Checkout code"
-        uses: actions/checkout@ec3a7ce113134d7a93b817d10a8272cb61118579
+        uses: actions/checkout@a12a3943b4bdde767164f792f33f40b04645d846
         with:
           persist-credentials: false