[ci] Bump go to 1.18

see goreleaser/goreleaser#3224

Author: phillbaker

.github/workflows/test.yml

@@ -24,7 +24,7 @@ jobs:
   test:
     strategy:
       matrix:
-        go-version: [1.16.x]
+        go-version: [1.18.x]
         os: [ubuntu-latest]
         es-major-version:
           - "6"
@@ -156,7 +156,7 @@ jobs:
     - name: Setup Go
       uses: actions/setup-go@v2
       with:
-        go-version: 1.16.x
+        go-version: 1.18.x
     - name: Import GPG key
       id: import_gpg
       uses: crazy-max/ghaction-import-gpg@v2