E0301 needs to be updated to new format

[sophiajt]

From: src/test/compile-fail/E0301.rs

E0301 needs a span_label, updating it from:

error[E0301]: cannot mutably borrow in a pattern guard
  --> src/test/compile-fail/E0301.rs:14:19
   |
14 |         option if option.take().is_none() => {}, //~ ERROR E0301
   |                   ^^^^^^

To:

error[E0301]: cannot mutably borrow in a pattern guard
  --> src/test/compile-fail/E0301.rs:14:19
   |
14 |         option if option.take().is_none() => {}, //~ ERROR E0301
   |                   ^^^^^^ borrowed mutably in pattern guard