[adc_ctrl,dv] adc_ctrl_clock_gating_vseq sometimes fails because we don't respond to alert pings when the clock is turned off

### Description

This is (hopefully!) the intended behaviour of the design, so it's really just showing that we need to be a bit more careful in the DV environment.

My suspicion is that we are making a mistake by allowing any alert pings to come out when the fast clock is turned off. This screenshot shows that we are sending pings when I think we probably shouldn't:

(there's a ping on the red cursor)

Start with the adc_ctrl_clock_gating_vseq sequence and inspect how alert pings are generated while the fast clock is off. Confirm the intended behavior from the failing scenario and adjust the DV handling so the sequence no longer fails on pings that should not be emitted.

Written by the indexing model from the issue text.