tests: use `testrepohg` in one more place in test-check-code.t This is already used elsewhere in the test to access the current hg repo, and avoids an error about the unknown `revlog-compression-zstd` when C extensions aren't built. The only other such error is in test-check-interfaces.py, but I don't see a way to avoid it other than to create an empty scratch repo. Differential Revision: https://phab.mercurial-scm.org/D9364

--- a/tests/test-check-code.t	Sat Nov 21 16:20:49 2020 -0500
+++ b/tests/test-check-code.t	Sat Nov 21 22:46:09 2020 -0500
@@ -90,6 +90,6 @@
 
 Keep Windows line endings in check
 
-  $ hg files 'set:eol(dos)'
+  $ testrepohg files 'set:eol(dos)'
   contrib/win32/hg.bat
   contrib/win32/mercurial.ini