verify: use some intermediate variables instead of a multi-liner

This is shorter and easier to read as the indentation remains the same.

Differential Revision: https://phab.mercurial-scm.org/D10813

mercurial/verify.py

@@ -361,12 +361,8 b' class verifier(object):'
                     # code (eg: hash verification, filename are ordered, etc.)
                     mfdelta = mfl.get(dir, n).read()
                 except Exception as inst:
-                    self._exc(
-                        lr,
-                        _(b"reading full manifest %s") % short(n),
-                        inst,
-                        label,
-                    )
+                    msg = _(b"reading full manifest %s") % short(n)
+                    self._exc(lr, msg, inst, label)
 
         if not dir:
             progress.complete()