chore(ci): add go1.21 to default test matrix

Author: mroth

.github/workflows/coverage.yml

@@ -9,6 +9,6 @@ jobs:
       - uses: actions/checkout@v3
       - uses: actions/setup-go@v4
         with:
-          go-version: "1.20"
+          go-version: "stable"
       - run: go test -coverprofile=coverage.txt -covermode=atomic
       - uses: codecov/codecov-action@v3

.github/workflows/test.yml

@@ -10,6 +10,7 @@ jobs:
           - "1.18"
           - "1.19"
           - "1.20"
+          - "1.21"
     name: Go ${{ matrix.go }} test
     steps:
       - uses: actions/checkout@v3