diagnostic: ignore FUSE-T files

FUSE-T is an alternative FUSE implementation for macOS.

Before:
```
% brew doctor
[...]
Warning: Some installed formulae are deprecated or disabled.
You should find replacements for the following formulae:
  sshfs-mac
  icu4c@76
  icu4c@77

Warning: Unbrewed dylibs were found in /usr/local/lib.
If you didn't put them there on purpose they could cause problems when
building Homebrew formulae and may need to be deleted.

Unexpected dylibs:
  /usr/local/lib/libfuse-t-1.0.49.dylib

Warning: Unbrewed '.pc' files were found in /usr/local/lib/pkgconfig.
If you didn't put them there on purpose they could cause problems when
building Homebrew formulae and may need to be deleted.

Unexpected '.pc' files:
  /usr/local/lib/pkgconfig/fuse-t.pc

Warning: Unbrewed static libraries were found in /usr/local/lib.
If you didn't put them there on purpose they could cause problems when
building Homebrew formulae and may need to be deleted.

Unexpected static libraries:
  /usr/local/lib/libfuse-t-1.0.49.a

Warning: You have uncommitted modifications to Homebrew/brew.
If this is a surprise to you, then you should stash these modifications.
Stashing returns Homebrew to a pristine state but can be undone
should you later need to do so for some reason.
  git -C "/opt/homebrew" stash -u && git -C "/opt/homebrew" clean -d -f

Uncommitted files:
  ?? Library/Homebrew/traildepot/.gitignore
  ?? Library/Homebrew/traildepot/config.textproto
[...]
```

After:
```
% brew doctor
[...]
Warning: Some installed formulae are deprecated or disabled.
You should find replacements for the following formulae:
  sshfs-mac
  icu4c@76
  icu4c@77

Warning: You have uncommitted modifications to Homebrew/brew.
If this is a surprise to you, then you should stash these modifications.
Stashing returns Homebrew to a pristine state but can be undone
should you later need to do so for some reason.
  git -C "/opt/homebrew" stash -u && git -C "/opt/homebrew" clean -d -f

Uncommitted files:
  ?? Library/Homebrew/traildepot/.gitignore
  ?? Library/Homebrew/traildepot/config.textproto
[...]
```

Resolves https://github.com/macos-fuse-t/fuse-t/issues/36.