Bump Go version to 1.18 for release and CI jobs

.github/workflows/go.yml

@@ -7,10 +7,10 @@ jobs:
     runs-on: ubuntu-latest
     steps:
 
-    - name: Set up Go 1.17
+    - name: Set up Go 1.18
       uses: actions/setup-go@v3
       with:
-        go-version: 1.17
+        go-version: 1.18
       id: go
 
     - name: Check out code into the Go module directory

.github/workflows/release.yaml

@@ -25,6 +25,6 @@ jobs:
         github_token: ${{ secrets.GITHUB_TOKEN }}
         goos: ${{ matrix.goos }}
         goarch: ${{ matrix.goarch }}
-        goversion: "https://golang.org/dl/go1.17.3.linux-amd64.tar.gz"
+        goversion: 1.18
         extra_files: LICENSE README.md smtprelay.ini
         ldflags: -s -w -X "main.appVersion=${{ env.APP_VERSION }}" -X "main.buildTime=${{ env.BUILD_TIME }}"