tests: gen_isr_table: filter *arm_mainline test on *_M_MAINLINE config

Since it was added, `arch.interrupt.gen_isr_table_local.arm_mainline`
filters on `CONFIG_ARMV6_M_ARMV8_M_BASELINE`. I'm not entirely sure whether
this was intentional, but this seems odd to me given a) the naming of the
test b) that the `platform_allow` is `qemu_cortex_m3` and c) that the
`arch.interrupt.gen_isr_table.arm_mainline` test it inherits part of its
config from filters on `CONFIG_ARMV7_M_ARMV8_M_MAINLINE`.

The current filtering setup also means that a command like
`west twister -c -T tests/kernel/gen_isr_table/` currently filters out all
of the `*gen_isr_table_local*` tests which was a surprise to me when
testing locally (no tests broke for a change I made as they were
all filtered out).

Assuming this is undesireable, change the filter to check against
`CONFIG_ARMV7_M_ARMV8_M_MAINLINE` to make it possible to run the tests
on the expected platform without needing to work around the filter.

Signed-off-by: Jonathon Penix <jpenix@quicinc.com>