git: also convert timezone to int (issue6359)

Credit to moshez for testing this in the wild.

Differential Revision: https://phab.mercurial-scm.org/D9062

hgext/git/gitlog.py

@@ -389,7 +389,7 b' class changelog(baselog):'
         sig = pygit2.Signature(
             encoding.unifromlocal(stringutil.person(user)),
             encoding.unifromlocal(stringutil.email(user)),
-            timestamp,
+            int(timestamp),
             -int(tz // 60),
         )
         oid = self.gitrepo.create_commit(