Add go 1.21 build/testing to github workflow (#457)

Author: t2y

.github/workflows/lint.yml

@@ -13,7 +13,7 @@ jobs:
     steps:
       - uses: actions/setup-go@v4
         with:
-          go-version: '1.20'
+          go-version: '1.21'
           cache: false
       - uses: actions/checkout@v3
       - name: golangci-lint

.github/workflows/pr.yml

@@ -10,6 +10,7 @@ jobs:
     strategy:
       matrix:
         go: [
+          '1.21',
           '1.20',
           '1.19',
           '1.18',