Update actions (#76)

This updates:
- actions/checkout to v3
- actions/setup-go to v4
- codecov/codecov-action to v3.

.github/workflows/go.yml

@@ -23,12 +23,12 @@ jobs:
 
     steps:
     - name: Setup Go
-      uses: actions/setup-go@v2
+      uses: actions/setup-go@v4
       with:
         go-version: ${{ matrix.go }}
 
     - name: Checkout code
-      uses: actions/checkout@v2
+      uses: actions/checkout@v3
 
     - name: Load cached dependencies
       uses: actions/cache@v1
@@ -45,4 +45,4 @@ jobs:
       run: make cover
 
     - name: Upload coverage to codecov.io
-      uses: codecov/codecov-action@v1
+      uses: codecov/codecov-action@v3