#24689 fix: resolve ShellCheck issues mentioned in #24675

Closes #24675

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Summary by cubic

Fixes ShellCheck warnings in git_push.sh by using safer empty checks and clearer messages. Updates the _common/git_push.sh.mustache template and regenerates sample scripts to apply the fix. Closes #24675.

• Bug Fixes
  • Replace [ "$var" = "" ] with [ -z "${var}" ] and keep quoted expansions.
  • Use braces in echoes and escape variable names in info logs (e.g., print ${git_host} literally).
  • Regenerate sample git_push.sh scripts across clients via ./bin/generate-samples.sh ./bin/configs/*.yaml.