Ignore generated arginfo for the ABI break label

[DanielEScherzer]

Description

Any objections? From the initial #15682

ABI breaks are not supposed to happen after feature freeze, i.e. when
the PHP API numbers have been bumped. To make it easier to notice
inadvertent ABI breaks, we automatically add an "ABI break" label to
all PRs which modify public (aka. installed) header files.

And I would consider arginfo to qualify as non-public header files

[DanielEScherzer]

CC @cmb69 @iluuu1994 @kocsismate

[iluuu1994]

Sounds good to me

[cmb69]

I'm fine with this as a stop-gap measure, but we should really stop installing headers which are not supposed to be public (see #16070).

[kocsismate]

Yes, I also think this make sense!