transaction: narrow the error filtering when failing to rename undo file

Having inconsistent "undo" files can be quite serious so we narrow the error
filtering to the intent that the comment explain.

(This is an opportunity improvement while looking at something next to that.)

Differential Revision: https://phab.mercurial-scm.org/D10845

mercurial/localrepo.py

@@ -3445,8 +3445,9 b' def aftertrans(files):'
             vfs.tryunlink(dest)
             try:
                 vfs.rename(src, dest)
-            except OSError:  # journal file does not yet exist
-                pass
+            except OSError as exc:  # journal file does not yet exist
+                if exc.errno != errno.ENOENT:
+                    raise
 
     return a