tests: arch: common: stack_unwind: fix symtab test

The symtab test should have the
`CONFIG_EXCEPTION_STACK_TRACE_SYMTAB` enabled. This was not
caught in the CI previously as the regex was also wrong, '['
and ']' are regex syntax and should be escaped.

Signed-off-by: Yong Cong Sin <ycsin@meta.com>