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/D10812

mercurial/verify.py

@@ -329,11 +329,8 b' class verifier(object):'
             if n in mflinkrevs:
                 del mflinkrevs[n]
             elif dir:
-                self._err(
-                    lr,
-                    _(b"%s not in parent-directory manifest") % short(n),
-                    label,
-                )
+                msg = _(b"%s not in parent-directory manifest") % short(n)
+                self._err(lr, msg, label)
             else:
                 self._err(lr, _(b"%s not in changesets") % short(n), label)