gdb/testsuite: avoid pointer values in test names

A test added in:

  commit 91eee81d23537366bb6072c66f662ab46d88380a
  Date:   Tue Jan 21 17:22:04 2025 +0000

      gdb: include NT_I386_TLS note in generated core files

includes a pointer value in the test name.  The value changes from run
to run making it harder to compare test results.  Fix this by giving
the test an actual name.

There's no change to what is being tested with the commit.