chore(deps): update golang docker tag to v1.21.6

See merge request https://gitlab.com/bonsai-oss/exporter/openzfs_exporter/-/merge_requests/27

.gitlab-ci.yml

@@ -17,7 +17,7 @@ include:
 
 compile:
   stage: build
-  image: golang:1.21.5-bullseye
+  image: golang:1.21.6-bullseye
   script:
     - mkdir -p binaries
     - go build -o binaries/openzfs_exporter-$(uname -s) ./cmd/openzfs_exporter/*.go