TST: Adding whatsnews entry and adding issue number in test (pandas-dev#21295)

Author: atulagrwl

doc/source/whatsnew/v0.24.0.txt

@@ -41,6 +41,7 @@ Other Enhancements
   (:issue:`21627`)
 - New method :meth:`HDFStore.walk` will recursively walk the group hierarchy of an HDF5 file (:issue:`10932`)
 - :meth:`Series.nlargest`, :meth:`Series.nsmallest`, :meth:`DataFrame.nlargest`, and :meth:`DataFrame.nsmallest` now accept the value ``"all"`` for the ``keep` argument. This keeps all ties for the nth largest/smallest value (:issue:`16818`)
+- New method :meth:`__git_version__` will return git commit sha of current build
 -
 
 .. _whatsnew_0240.api_breaking:

pandas/tests/test_common.py

@@ -265,7 +265,7 @@ def test_compression_warning(compression_only):
             with f:
                 df.to_csv(f, compression=compression_only)
 
-
+# GH 21295
 def test_git_version():
     git_version = pd.__git_version__
     assert len(git_version) == 40