Chore: Upgrade runners to Ubuntu 26.04 (#14347)

* Moves runners to 26.04 and a few jobs to -slim variant

* Probably fixing the imagemagik 7 problems and maybe the frontend playwright thing?

* Compare thumbnails, but allow a little difference in the perceptual hash

.github/workflows/issue-bot.yml

@@ -7,7 +7,7 @@ jobs:
     # Note: peakoss/anti-slop does not support the `issues` event yet (all of its
     # issue inputs are still commented out upstream), so the checks that the PR Bot
     # workflow gets from the action are implemented manually here.
-    runs-on: ubuntu-latest
+    runs-on: ubuntu-slim
     permissions:
       issues: write
     steps: