[pre-commit] Add codespell-clean gdb subdirs

[pre-commit] Add codespell-clean gdb subdirs

As an alternative to adding the gdb dir to codespell while it's still not
codespell-clean [1], add gdb subdirs which are codespell-clean.

Found using:
...
$ for d in $(find gdb -maxdepth 1 -type d | egrep -v "testsuite|gdb$"); do \
      echo -n "$d: "; \
      codespell --config gdb/contrib/setup.cfg $d 2>/dev/null \
          | wc -l; \
  done 2>&1 \
      | grep ": 0"
gdb/tui: 0
gdb/target: 0
gdb/data-directory: 0
gdb/po: 0
gdb/system-gdbinit: 0
gdb/mi: 0
gdb/syscalls: 0
gdb/arch: 0
gdb/regformats: 0
gdb/compile: 0
...

Verified using:
...
$ pre-commit run codespell --all-files
codespell................................................................Passed
...

Approved-By: Tom Tromey <tom@tromey.com>
[1] https://sourceware.org/pipermail/gdb-patches/2025-March/216781.html