gdb/testsuite: fix typo 'unsupport' to 'unsupported'

I noticed that in commit:

  commit 5cabc8098e65ac22d4245232ad20b19fa4729802
  Date:   Wed Jul 31 15:55:57 2024 +0100

      gdb/python: implement Python find_exec_by_build_id hook

I managed to typo 'unsupported' as 'unsupport'.  If you run the test
on a target that doesn't support core file creation then you'll get a
TCL error.

Fixed in this commit.