[REF][PHP8.2] Declare system property in tests

[braders]

Overview

Declare system property in tests.

Before

3 tests were declaring $this->system as a dynamic property, which is deprecated in PHP8.2

After

Propery is decalared on the affected classes, PHP 8.2 compatiable.

These are tests so there should hopefully be no backwards compatability impact.

[civibot]

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[totten]

civibot, test this pleas

[totten]

civibot, test this please