gdb/testsuite: accept variable number of spaces in gdb.base/jit-reader-simple.exp regex

I see this failure:

    FAIL: gdb.base/jit-reader-simple.exp: standalone: change addr: initial run: maint info breakpoints shows jit breakpoint

The jit breakpoint expected by the test is there, it's just that the
number of spaces doesn't match what the test expects, after "jit
events":

    -2      jit events       keep y   0x0000555555555119 <__jit_debug_register_code> inf 1

Fix that by relaxing the regex a bit.

Change-Id: Ia3b04e6d5978399d940fd1a590f95f15275ca7ac