[gdb/testsuite] Fix gdb.ada/out_of_line_in_inlined.exp with -m32 and gcc-10

When running test-case gdb.ada/out_of_line_in_inlined.exp with target board
unix/-m32 on a system with gcc-10 default compiler, we run into:
...
(gdb) break foo_o224_021.child1.child2^M
Breakpoint 1 at 0x804ba59: foo_o224_021.child1.child2. (3 locations)^M
(gdb) FAIL: gdb.ada/out_of_line_in_inlined.exp: scenario=all: \
  break foo_o224_021.child1.child2
...

The test does not expect the "3 locations" part.

Fix this by using gdb_breakpoint instead of gdb_test.

Tested on x86_64-linux.

gdb/testsuite/ChangeLog:

2021-01-28  Tom de Vries  <tdevries@suse.de>

	* gdb.ada/out_of_line_in_inlined.exp: Use gdb_breakpoint.