Update verifyFreezePeriod.yml to consider milestone promotions not as error

[vogella]

From eclipse-platform/eclipse.platform.ui#1967 (comment)

Milestones don't have freezes but there is still the "promotion" day in the calendar (so everyone can see when it is) and the script checking it

eclipse.platform.releng.aggregator/.github/workflows/verifyFreezePeriod.yml

Line 22 in 42b625b

curl "${calURL}" | grep -i -e "stabilization" -e "signoff" -e "promotion"

doesn't distinguish between M, RC and R promotion thus we end up with this freezes during M promotion days. It would be nice if someone enhances the script to not complain for milestone promotions.

[vogella]

@sratz and @HannesWell you worked on this script before. Could you update it so that milestone promotions are not reported as freezes?

[vogella]

Thanks @sratz and @HannesWell