Update actions/checkout requirement to v2.3.4

Updates the requirements on [actions/checkout](https://github.com/actions/checkout) to permit the latest version.
- [Release notes](https://github.com/actions/checkout/releases)
- [Changelog](https://github.com/actions/checkout/blob/main/CHANGELOG.md)
- [Commits](5a4ac9002d)

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

.github/workflows/build.yml

@@ -13,7 +13,7 @@ jobs:
 
     steps:
     - name: Checkout code
-      uses: actions/checkout@v1
+      uses: actions/checkout@v2.3.4
 
     - name: Set up Ruby ${{ matrix.ruby }}
       uses: actions/setup-ruby@v1

.github/workflows/gempush.yml

@@ -10,7 +10,7 @@ jobs:
     runs-on: ubuntu-latest
 
     steps:
-    - uses: actions/checkout@master
+    - uses: actions/checkout@v2.3.4
     - name: Set up Ruby 2.6
       uses: actions/setup-ruby@v1
       with: