chore: run extended suite on PRs for critical areas (#18088)

## Which issue does this PR close?

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- Closes #.
Related to #18084

## Rationale for this change

Run extended suite on PRs for critical areas, to avoid post merge
bugfixing

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---------

Co-authored-by: Andrew Lamb <andrew@nerdnetworks.org>

Author: comphead

.github/workflows/extended.yml

@@ -36,6 +36,14 @@ on:
       # it is not expected to have many changes in these branches,
       # so running extended tests is not a burden
       - 'branch-*'
+  # Also run for changes to some critical areas that are most likely
+  # to trigger errors in extended tests
+  pull_request:
+    branches: [ '**' ]
+    paths:
+      - 'datafusion/physical*/**/*.rs'
+      - 'datafusion/expr*/**/*.rs'
+      - 'datafusion/optimizer/**/*.rs'
   workflow_dispatch:
     inputs:
       pr_number: