Fix certificate filtering

This is a regression from 25d9df5c

filterRegExp must not be ported to filterRegularExpression in Qt5

setFilterFixedString sets filterRegExp, but not filterRegularExpression

In Qt6 this is fixed.

Since we are only interested in filerting fixed strings just pass the pattern to the QString calls below
2 jobs for !14 with work/fixfiltering in 5 minutes and 9 seconds (queued for 4 minutes and 44 seconds)
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