Make the pyrefly job blocking

The tree is clean under it now, so the job can fail the run and catch the next
async regression instead of only reporting one.

Nothing is suppressed beyond the two ignores that state their reason at the
line, for an async __new__ and an untyped callback registry, neither of which
pyrefly can model.

.github/workflows/ci.yml

@@ -55,11 +55,6 @@ jobs:
   pyrefly:
     name: Pyrefly (async correctness)
     runs-on: ubuntu-latest
-    # Advisory for now: the tree still has findings, a good number of them
-    # real bugs, so this reports without failing the run. It also means an
-    # install failure or a checker crash passes silently. Remove the line once
-    # the findings are dealt with, which is the point of having it.
-    continue-on-error: true
     steps:
       - uses: actions/checkout@v7
       - uses: facebook/pyrefly@main