Update actions/checkout requirement to v2.3.1

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/master/CHANGELOG.md)
- [Commits](28c7f3d2b5)

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

.github/workflows/acctest.yml

@@ -23,7 +23,7 @@ jobs:
       id: go
 
     - name: Check out code into the Go module directory
-      uses: actions/checkout@v1
+      uses: actions/checkout@v2.3.1
 
     - name: Get dependencies
       run: |
@@ -58,7 +58,7 @@ jobs:
       id: go
 
     - name: Check out code into the Go module directory
-      uses: actions/checkout@v1
+      uses: actions/checkout@v2.3.1
 
     # TODO: convert this to `services`
     - name: Start Unifi controller

.github/workflows/release.yml

@@ -10,7 +10,7 @@ jobs:
     steps:
       -
         name: Checkout
-        uses: actions/checkout@v2
+        uses: actions/checkout@v2.3.1
       -
         name: Unshallow
         run: git fetch --prune --unshallow