[8.x] Add missing singular minute() call

[owenvoke]

It looks like a minute() call was missed out from #38815, however I'm not entirely sure if this was intentional.

This works the same way as the existing singular calls for the other Wormhole methods:

// Before
$this->travel(1)->minutes();
$this->travel(-1)->minutes();

// After
$this->travel(1)->minute();
$this->travel(-1)->minute();