Fix regex pattern for tagged rust warnings in compilation output

[ensc]

Rust now emits warnings with optional tags (e.g., "warning[E0133]:"). Update the warning regex pattern to match the approach already used for error patterns, which handle the same tagged format.

The pattern now accepts optional content between 'warning' and the colon, matching the existing error pattern that handles 'error[^:]*:'.

Fixes: #121

[ensc]

I think, the CI errors

eask package
💡 Unmatched version `3.5`; it should be `3.4`
💡 URL header is optional, but it's often recommended
💡 Unmatched keyword `languages`; add `(keywords "languages")` to Eask-file or consider removing it
💡 Unmatched dependency `emacs`; add `(depends-on "emacs")` to Eask-file or consider removing it
💡 Unmatched dependency `let-alist`; add `(depends-on "let-alist")` to Eask-file or consider removing it
💡 Unmatched dependency `flycheck`; add `(flycheck "VERSION")` to package-file or consider removing it
Loading package information... done ✓
- [1/1] Installing package-build (20260115.1042)... done ✓
Building artifact rustic (3.5)...

Debugger entered--Lisp error: (wrong-type-argument stringp nil)
string-match("\\`\\(http\\)://\\(?:codeberg\\.org\\|git\\(?:\\.sr\\.ht\\|\\..." nil)

are caused by something else (missing metadata required by recent eask?)

[CeleritasCelery]

yes, I just ran the CI and it is failing. It has not been run in a while so something is broken.