updated github workflow to use go 1.21

.github/workflows/ci.yml

@@ -9,16 +9,13 @@ jobs:
       fail-fast: false
       matrix:
         os: [ ubuntu-latest, macos-latest, windows-latest ]
-        go: [ '1.19', '1.20' ]
+        go: [ '1.21']
 
         include:
           # Set the minimum Go patch version for the given Go minor
           # Usable via ${{ matrix.GO_SEMVER }}
-          - go: '1.19'
-            GO_SEMVER: '~1.19.9'
-
-          - go: '1.20'
-            GO_SEMVER: '~1.20.4'
+          - go: '1.21'
+            GO_SEMVER: '1.21.7'
 
           # Set some variables per OS, usable via ${{ matrix.VAR }}
           # CADDY_BIN_PATH: the path to the compiled Caddy binary, for artifact publishing
@@ -43,7 +40,7 @@ jobs:
       - name: Set up Go
         uses: actions/setup-go@v3
         with:
-          go-version: 1.19
+          go-version: 1.21
 
       - name: Build
         run: go build -v ./...