chore: update merge request template

---

• Target branch: main
• Changes should be cherry-picked to 24.1: no
• Staging: https://docs.binary.picodata.io/picodata/merge-request-template/

.gitlab/merge_request_templates/default.md

-
 ---
 - Close #...
-- Target branch: %{target_branch}
-- Changes should be cherry-picked to 24.1: yes / no
-- Staging: https://docs.binary.picodata.io/picodata/branch-.../
+- Target branch: `%{target_branch}`
+- Changes should be cherry-picked to `24.2`: yes / no
+- Staging: https://docs.binary.picodata.io/picodata/%{source_branch}/
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