patch: fix import-time syntax error in test-check-module-imports.t

This is more correct, though we were getting lucky in practice with
our rewriter saving us.

# skip-blame just a b prefix

Differential Revision: https://phab.mercurial-scm.org/D3584

mercurial/patch.py

@@ -51,7 +51,7 b' stringio = util.stringio'
 gitre = re.compile(br'diff --git a/(.*) b/(.*)')
 tabsplitter = re.compile(br'(\t+|[^\t]+)')
 wordsplitter = re.compile(br'(\t+| +|[a-zA-Z0-9_\x80-\xff]+|'
-                          '[^ \ta-zA-Z0-9_\x80-\xff])')
+                          b'[^ \ta-zA-Z0-9_\x80-\xff])')
 
 PatchError = error.PatchError