gdb/testsuite: update a pattern in gdb_file_cmd

gdb/testsuite: update a pattern in gdb_file_cmd

When building GDB with the following CFLAGS and CXXFLAGS as part of
configure line:

    CFLAGS=-std=gnu11 CXXFLAGS=-std=gnu++11

Then run the selftest.exp, I see:

======
Running /home/lee/dev/binutils-gdb/gdb/testsuite/gdb.gdb/selftest.exp
...
FAIL: gdb.gdb/selftest.exp: run until breakpoint at captured_main
WARNING: Couldn't test self

                === gdb Summary ===

 # of unexpected failures        1
/home/lee/dev/binutils-gdb/gdb/gdb version  13.0.50.20221206-git -nw -nx
-iex "set height 0" -iex "set width 0" -data-directory
/home/lee/dev/binutils-gdb/gdb/testsuite/../data-directory
======

It is the fact that when I use the previously mentioned CFLAGS and
CXXFLAGS as part of the configuration line, the default value (-O2 -g)
is overridden, then GDB has no debug information.  When there's no debug
information, GDB should not run the testcase in selftest.exp.

The root cause of this FAIL is that the $gdb_file_cmd_debug_info didn't
get the right value ("nodebug") during the gdb_file_cmd procedure.

That's because in this commit,

  commit 3453e7e409f44a79ac6695589836edb8a49bfb08
  Date:   Sat May 19 11:25:20 2018 -0600

    Clean up "Reading symbols" output

It changed "no debugging..." to "No debugging..." which causes the above
problem.  This patch only updates the corresponding pattern to fix this
issue.

With this patch applied, I see:

======
Running /home/lee/dev/binutils-gdb/gdb/testsuite/gdb.gdb/selftest.exp
...

                === gdb Summary ===

 # of untested testcases         1
/home/lee/dev/binutils-gdb/gdb/gdb version  13.0.50.20221206-git -nw -nx
-iex "set height 0" -iex "set width 0" -data-directory
/home/lee/dev/binutils-gdb/gdb/testsuite/../data-directory
======

Tested on x86_64-linux.

Approved-By: Simon Marchi <simon.marchi@efficios.com>