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/D10808

mercurial/verify.py

@@ -153,11 +153,8 b' class verifier(object):'
         try:
             p1, p2 = obj.parents(node)
             if p1 not in seen and p1 != self.repo.nullid:
-                self._err(
-                    lr,
-                    _(b"unknown parent 1 %s of %s") % (short(p1), short(node)),
-                    f,
-                )
+                msg = _(b"unknown parent 1 %s of %s") % (short(p1), short(node))
+                self._err(lr, msg, f)
             if p2 not in seen and p2 != self.repo.nullid:
                 self._err(
                     lr,