test-command-template: glob out detailed "invalid escape" message

Python 3 also reports the position where an invalid escape found.

contrib/python3-whitelist

@@ -36,6 +36,7 test-children.t
 test-clone-pull-corruption.t
 test-clone-r.t
 test-clone-update-order.t
+test-command-template.t
 test-commit-amend.t
 test-commit-unresolved.t
 test-commit.t

tests/test-command-template.t

@@ -4438,7 +4438,7 Test broken string escapes:
   hg: parse error: trailing \ in string
   [255]
   $ hg log -T "\\xy" -R a
-  hg: parse error: invalid \x escape
+  hg: parse error: invalid \x escape* (glob)
   [255]
 
 json filter should escape HTML tags so that the output can be embedded in hgweb: