Rollup merge of #144733 - Muscraft:secondary-file-sigil, r=compiler-errors

fix: Match width of ascii and unicode secondary file start

The current [unicode secondary file start](https://github.com/rust-lang/rust/blob/64ca23b6235732fa61c0a2b957c5d7e591e7c972/compiler/rustc_errors/src/emitter.rs#L2991) is only three characters, whereas the ASCII variant and normal [file start](https://github.com/rust-lang/rust/blob/64ca23b6235732fa61c0a2b957c5d7e591e7c972/compiler/rustc_errors/src/emitter.rs#L2983-L2984) are four characters. This slight difference caused the paths following a Unicode secondary file start to not align with other structured elements.

Author: jdonszelmann