Merge branch 'sh-add-golang-1.21' into 'main'

Add Go v1.21 to CI

See merge request https://gitlab.com/gitlab-org/gitlab-shell/-/merge_requests/829



Merged-by: Igor Drozdov <idrozdov@gitlab.com>
Approved-by: Igor Drozdov <idrozdov@gitlab.com>
Co-authored-by: Stan Hu <stanhu@gmail.com>

.gitlab-ci.yml

@@ -78,7 +78,7 @@ default:
 .go-matrix-job:
   parallel:
     matrix:
-      - GO_VERSION: ["golang-1.19", "golang-1.20"]
+      - GO_VERSION: ["golang-1.19", "golang-1.20", "golang-1.21"]
 
 ################################################################################
 # Prepare jobs