Add coverage input to reusable-testing #1208

Job	Run time
test / Get base test matrix	4s
test / Prepare matrix for unit tests	5s
test / Prepare matrix for functional tests	3s
test / Functional - WP ${{ matrix.wp }} on PHP ${{ matrix.php }} with ${{ matrix.dbtype != 'sqlite' && matrix.mysql \|\| 'SQLite' }}${{ matrix.coverage && ' (with coverage)' \|\| '' }}	0s
test / Unit test / PHP ${{ matrix.php }}${{ matrix.coverage && ' (with coverage)' \|\| '' }}	0s
	12s

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