I have error or warning messages from some tool with the following format:  
```
2022-08-18T21:25:01.972 WARNING ##]  file:///Users/myuser/somedir/file.txt:123: Error: something went wrong
```

One of the built-in error formats erroneously matched the leading timestamp and `file://` as part of the file name. I need a format that ignores all of the stuff in the beginning but can’t come up with one. I don’t quite understand the advanced options from `:h errorformat`.
The version I have is this but it of course includes the beginning of the line in the file name as well: `%f:%l:\ %t%*\\a:\ %m`.

How can I fix my errorformat so that only the actual file name is matched?

i.e. this:   `/Users/myuser/somedir/file.txt`