tests: add b'' prefixes to flagprocessorext.py

Otherwise a part of test-flavprocessor.t fails due to not
setting the proper key.

Differential Revision: https://phab.mercurial-scm.org/D5724

tests/flagprocessorext.py

@@ -107,7 +107,7 b' def extsetup(ui):'
 
     # Teach exchange to use changegroup 3
     for k in exchange._bundlespeccontentopts.keys():
-        exchange._bundlespeccontentopts[k]["cg.version"] = "03"
+        exchange._bundlespeccontentopts[k][b"cg.version"] = b"03"
 
     # Register flag processors for each extension
     revlog.addflagprocessor(