Don't require whitespace right after match

[isidentical]

Summary

Fixes #627. This check seems like preventing something that is allowed in the regular Python.

Test Plan

Added a test which didn't work before this patch.

[codecov-commenter]

Codecov Report

Merging #628 (50476f7) into main (2345848) will increase coverage by 0.00%.
The diff coverage is n/a.

@@           Coverage Diff           @@
##             main     #628   +/-   ##
=======================================
  Coverage   94.78%   94.79%           
=======================================
  Files         245      245           
  Lines       25256    25254    -2     
=======================================
- Hits        23940    23939    -1     
+ Misses       1316     1315    -1     

Impacted Files	Coverage Δ
libcst/_nodes/statement.py	95.21% <ø> (+0.06%)	⬆️
libcst/_nodes/tests/test_match.py	100.00% <ø> (ø)

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[stroxler]

Looks good to me, thanks for catching the bug!