templates: Improve warnings for abandoned issues.

The new language aims to be brief while still providing some motivation for
what's happening.

Author: alya

config/templates/abandonWarning.md

@@ -1,5 +1 @@
-Hello @{assignee}, you have been unassigned from this issue because you have not updated this issue or any referenced pull requests for over {total} days.
-
-You can reclaim this issue or claim any other issue by commenting `@{username} claim` on that issue.
-
-Thanks for your contributions, and hope to see you again soon!
+@{assignee} You have been unassigned from this issue because you have not made any updates for over {total} days. Please feel free to reclaim the issue if you decide to pick up again. Thanks!

config/templates/inactiveWarning.md

@@ -1,9 +1,5 @@
-Hello @{assignee}, you claimed this issue to work on it, but this issue and any referenced pull requests haven't been updated for {remind} days. Are you still working on this issue?
+@{assignee} We noticed that you have not made any updates to this issue or linked PRs for {remind} days. Please comment here if you are still actively working on it. Otherwise, we'd appreciate a quick `@{username} abandon` comment so that someone else can claim this issue and continue from where you left off.
 
-If so, please update this issue by leaving a comment on this issue to let me know that you're still working on it. Otherwise, I'll automatically remove you from this issue in {abandon} days.
-
-If you've decided to work on something else, simply comment `@{username} abandon` so that someone else can claim it and continue from where you left off.
-
-Thank you for your valuable contributions to Zulip!
+If we don't hear back, you will be automatically unassigned in {abandon} days. Thanks!
 
 <!-- inactiveWarning -->