Use pandas 2.1.4 for diff.

2.2.0 introduces a regression in the use of melt that this script
relies on.

.github/workflows/build-member.yml

@@ -239,5 +239,5 @@ jobs:
       working-directory: ${{ github.workspace }}/conformance
       shell: bash
       run: |
-        python -m pip install pandas packaging
+        python -m pip install pandas==2.1.4 packaging
         python ./diff.py -s conformance_expected_output.csv github.csv

.github/workflows/run-cts-pr.yml

@@ -164,7 +164,7 @@ jobs:
     - name: Diff Conformance Test
       shell: bash
       run: |
-        python -m pip install pandas packaging
+        python -m pip install pandas==2.1.4 packaging
         python conformance/diff.py -s conformance/conformance_expected_output.csv github.csv
 
     - name: Upload conformance output artifact

conformance/diff.py

@@ -8,6 +8,13 @@
   print("This script requires the use of Pandas v1.1.0.")
   sys.exit(1)
 
+# melt() with a MultiIndex is not working as of 2.2.0. Force use of an earlier
+# version for now until the regression is corrected or we fix this script.
+# See: https://github.com/pandas-dev/pandas/issues/57663
+if Version(pd.__version__) >= Version("2.2.0"):
+  print("This script does not support Pandas v2.2.0.")
+  sys.exit(1)
+
 # Argument parser
 parser = argparse.ArgumentParser()
 parser.add_argument("csv1", type = str, help="First CSV")