Unrolled build for rust-lang#126501

Rollup merge of rust-lang#126501 - lqd:fix-pr-template, r=Mark-Simulacrum

make bors ignore comments in PR template

As discussed [here](https://rust-lang.zulipchat.com/#narrow/stream/122651-general/topic/default.20PR.20description.20feedback/near/444794577), the existing PR template is not yet ignored by bors and the html comments show up in git history.

This PR uses markers so the html comments are deleted by the bot.

r? lcnr

.github/pull_request_template.md

@@ -1,3 +1,4 @@
+<!-- homu-ignore:start -->
 <!--
 If this PR is related to an unstable feature or an otherwise tracked effort,
 please link to the relevant tracking issue here. If you don't know of a related
@@ -7,4 +8,5 @@ This PR will get automatically assigned to a reviewer. In case you would like
 a specific user to review your work, you can assign it to them by using
 
     r​? <reviewer name>
--->
+-->
+<!-- homu-ignore:end -->