GitHub Actions: upgrade actions, setup CODECOV_TOKEN

.github/workflows/go.yaml

@@ -6,11 +6,12 @@ jobs:
     name: Test Go ${{ matrix.go }}
     runs-on: ubuntu-latest
     env:
-      go_latest: '1.20'
+      go_latest: 'stable'
     strategy:
       matrix:
         go:
-        - '1.20'
+        - 'stable'
+        - 'oldstable'
         - '1.19'
         - '1.18'
         - '1.17'
@@ -23,10 +24,10 @@ jobs:
     steps:
 
     - name: Check out code into the Go module directory
-      uses: actions/checkout@v3
+      uses: actions/checkout@v4
 
     - name: Set up Go ${{ matrix.go }}
-      uses: actions/setup-go@v4
+      uses: actions/setup-go@v5
       with:
         go-version: ${{ matrix.go }}
 
@@ -36,4 +37,6 @@ jobs:
     # https://app.codecov.io/github.com/dolmen-go/jsonptr
     - name: Upload coverage to Codecov
       if: matrix.go == env.go_latest
-      uses: codecov/codecov-action@v3
+      uses: codecov/codecov-action@v4
+        with:
+          token: ${{ secrets.CODECOV_TOKEN }}