diagnostic: elide stray filenames in subdirs

[gromgit]

Usually, the subdirectory name is sufficient info, and the full file list is just noise.

This reduces brew doctor output clutter, making it easier for user to paste, and maintainers to parse.

Before:

$ brew doctor
[...]
Unexpected header files:
  /usr/local/include/node/cppgc/allocation.h
  /usr/local/include/node/cppgc/common.h
  /usr/local/include/node/cppgc/custom-space.h
  /usr/local/include/node/cppgc/garbage-collected.h
  /usr/local/include/node/cppgc/heap.h
  /usr/local/include/node/cppgc/internal/accessors.h
  /usr/local/include/node/cppgc/internal/api-constants.h
  /usr/local/include/node/cppgc/internal/compiler-specific.h
  /usr/local/include/node/cppgc/internal/finalizer-trait.h
  /usr/local/include/node/cppgc/internal/gc-info.h
  /usr/local/include/node/cppgc/internal/logging.h
  /usr/local/include/node/cppgc/internal/persistent-node.h
  /usr/local/include/node/cppgc/internal/pointer-policies.h
  /usr/local/include/node/cppgc/internal/prefinalizer-handler.h
[about 500 more files]

After:

$ brew doctor
Unexpected header files:
  /usr/local/include/node/*

The full list of stray files can still be viewed with brew doctor -v.

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[MikeMcQuaid]

Thanks, looks good! Feel free to merge as-is without a rereview if you accept the suggestion as-is.

[MikeMcQuaid]

Thanks again @gromgit!