fix: Match width of ascii and unicode secondary file start

compiler/rustc_errors/src/emitter.rs

@@ -2988,7 +2988,7 @@ impl HumanEmitter {
     fn secondary_file_start(&self) -> &'static str {
         match self.theme {
             OutputTheme::Ascii => "::: ",
-            OutputTheme::Unicode => " ⸬ ",
+            OutputTheme::Unicode => " ⸬  ",
         }
     }
 

tests/ui/error-emitter/close_window.unicode.stderr

@@ -4,7 +4,7 @@ error[E0624]: method `method` is private
 LL │     s.method();
    │       ━━━━━━ private method
    │
-   ⸬ $DIR/auxiliary/close_window.rs:3:5
+   ⸬  $DIR/auxiliary/close_window.rs:3:5
    │
 LL │     fn method(&self) {}
    ╰╴    ──────────────── private method defined here