tests: alter email `From` line to a value that's consistently parsed

Python2:
>>> email.header.decode_header('=?UTF-8?q?Rapha=C3=ABl=20Hertzog?= <[e-mail]>')
[('Rapha\xc3\xabl Hertzog', 'utf-8'), ('<[e-mail]>', None)]

Python3:
>>> email.header.decode_header('=?UTF-8?q?Rapha=C3=ABl=20Hertzog?= <[e-mail]>')
[(b'Rapha\xc3\xabl Hertzog', 'utf-8'), (b' <[e-mail]>', None)]

So alter the input to an input that parses to the same result
consistently. After skimming the relevant RFC (1342), I'm not sure if
what we had was valid, or how I could modify it to be more consistent.

Differential Revision: https://phab.mercurial-scm.org/D5769

contrib/python3-whitelist

@@ -311,6 +311,7 b' test-impexp-branch.t'
 test-import-bypass.t
 test-import-context.t
 test-import-eol.t
+test-import-git.t
 test-import-merge.t
 test-import-unknown.t
 test-import.t

tests/test-import-git.t

@@ -826,7 +826,7 b' Test email metadata'
 
   $ hg revert -qa
   $ hg --encoding utf-8 import - <<EOF
-  > From: =?UTF-8?q?Rapha=C3=ABl=20Hertzog?= <[e-mail]>
+  > From: =?utf-8?q?Rapha=C3=ABl_Hertzog_=3Chertzog=40debian=2Eorg=3E?=
   > Subject: [PATCH] =?UTF-8?q?=C5=A7=E2=82=AC=C3=9F=E1=B9=AA?=
   > 
   > diff --git a/a b/a