Auto merge of #29255 - delan:clean-up-workflow-names, r=mrobinson

CI: clean up workflow names

The workflow names on [the actions page](https://github.com/servo/servo/actions) could be a bit clearer and more consistent.

This patch gives main.yml and pull-request.yml more meaningful names, clarifies the nightly builds, and groups the WPT-related builds in lexicographic order.

---
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- [ ] ~~`./mach test-tidy` does not report any errors~~
- [ ] These changes fix #___ (GitHub issue number if applicable)

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- [ ] There are tests for these changes OR
- [x] These changes do not require tests because they affect the CI configuration

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.github/workflows/main.yml

@@ -1,4 +1,4 @@
-name: CI
+name: Merge queue and try
 
 on:
   # Triggers the workflow on push events but only for the master branch