[php8-compat] Fix php beautifier notice by conditionally assinging dy…

[seamuslee001]

…namic foreign key to the template

Overview

This fixes the warnings in a similar vein to #20445

Before

PHP Beautifier warnings generated

After

No warnings

ping @eileenmcnaughton @totten @colemanw @demeritcowboy

[civibot]

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[eileenmcnaughton]

my instinct was to do this instead

   $table['dynamicForeignKey'] = $dynamicForeign ?? '';

but that's bikeshedding