[gdb/testsuite] Fix gdb.ada/excep_handle.exp for updated gdb_test

[gdb/testsuite] Fix gdb.ada/excep_handle.exp for updated gdb_test

Test-case gdb.ada/excep_handle.exp fails since commit e2f620135d9
("gdb/testsuite: change newline patterns used in gdb_test"):
...
(gdb) continue^M
Continuing.^M
^M
Catchpoint 2, exception at 0x00000000004020b6 in foo () at foo.adb:26^M
26            when Constraint_Error =>^M
(gdb) FAIL: gdb.ada/excep_handle.exp: continuing to first Constraint_Error \
  exception handlers
...

The output is supposed to be matched by:
...
gdb_test "continue" \
         "Continuing\.$eol$catchpoint_constraint_error_msg$eol.*" \
         "continuing to first Constraint_Error exception handlers"
...
but the $eol bit no longer matches due to the stricter matching introduced
in aforementioned commit.

Fix this by dropping the "$eol.*" bit.

Tested on x86_64-linux.

PR testsuite/30399
Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=30399