fix: revert to GO_VERSION env var for Go version

Runtime.Goversion is not available in GoReleaser templates.
Use environment variable approach as before.

Author: jackspirou

.goreleaser.yaml

@@ -41,7 +41,7 @@ builds:
       - -X main.version={{.Version}}
       - -X main.commit={{.ShortCommit}}
       - -X main.buildDate={{.Date}}
-      - -X main.goVersion={{.Runtime.Goversion}}
+      - -X main.goVersion={{.Env.GO_VERSION}}
       - -X main.builtBy=goreleaser
 
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