fix: go get fails with GO_GET_CLONE_URL_PROTOCOL=ssh on the default SSH port (#39674)

Go rejects scp-style addresses like `git@host:owner/repo.git` in the
go-import meta tag because they have no URL scheme, so
GO_GET_CLONE_URL_PROTOCOL=ssh did not work with the default SSH port
unless USE_COMPAT_SSH_URI was set. Always use the ssh:// form for
go-get.

When DISABLE_HTTP_GIT is enabled, the https clone URL can never work, so
GO_GET_CLONE_URL_PROTOCOL now defaults to ssh in that case.

---------

Co-authored-by: wxiaoguang <wxiaoguang@gmail.com>

custom/conf/app.example.ini

@@ -1095,8 +1095,9 @@ LEVEL = Info
 ;; Force ssh:// clone url instead of scp-style uri when default SSH port is used
 ;USE_COMPAT_SSH_URI = false
 ;;
-;; Value for the "go get" request returns the repository url as https or ssh, default is https
-;GO_GET_CLONE_URL_PROTOCOL = https
+;; Scheme of the returned URL for the "go get" response.
+;; Default is "https" if DISABLE_HTTP_GIT=false or SSH is disabled, otherwise "ssh".
+;GO_GET_CLONE_URL_PROTOCOL =
 ;;
 ;; Close issues as long as a commit on any branch marks it as fixed
 ;DEFAULT_CLOSE_ISSUES_VIA_COMMITS_IN_ANY_BRANCH = false