gdb/testsuite: give a test a real name

gdb/testsuite: give a test a real name

A test in gdb.python/py-send-packet.exp added in this commit:

  commit 24b2de7b776f8f23788d855b1eec290c6e208821
  Date:   Tue Aug 31 14:04:36 2021 +0100

      gdb/python: add gdb.RemoteTargetConnection.send_packet

included a large amount of binary data in the command sent to GDB.  As
this test didn't have a real test name the binary data was included in
the gdb.sum file.  The contents of the binary data could change
between different runs of GDB, and this makes comparing results
harder.

This commit gives the test a real test name.