Switch static var to using Civi::statics

[eileenmcnaughton]

Overview

Switches a static var from in-function to using civi statics

Before

static var in function

After

Using Civi statics for static function

Technical Details

This static variable is actually problematic. Moving it to statics will allow us to stop reseting it
in the test suite & to hone in on where it is actually broken rather than the test suite
is not flushing it

Comments

[civibot]

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[eileenmcnaughton]

Note this is mergeable as is but I'm looking at fully removing the static in #16139 - still good to merge this in the meantime in case that stalls