ci: start integrating go 1.18 into the CI pipelines

.gitlab-ci.yml

@@ -55,23 +55,19 @@ default:
   script:
     - make verify test
 
-go:1.16:
+tests:
   extends: .test
-  image: golang:1.16
-  after_script:
-    - make coverage
-  coverage: '/\d+.\d+%/'
-
-go:1.17:
-  extends: .test
-  image: golang:1.17
+  image: golang:${GO_VERSION}
+  parallel:
+    matrix:
+      - GO_VERSION: ["1.16", "1.17", "1.18"]
   after_script:
     - make coverage
   coverage: '/\d+.\d+%/'
 
 race:
   extends: .test
-  image: golang:1.17
+  image: golang:1.18
   script:
     - make test_golang_race