Fix include(/regexp/) when used without a count.

[JonRowe]

Fixes #1481 there was a bug where a regexp and a count contraint would work with the include matcher, but not a bare regexp e.g.

# worked
expect("astring").to include(/a/).once

# failed
expect("astring").to include(/a/)

This makes this consistent with the docs as working, in another version of RSpec we may look to deprecate this usage as it is not doing an include? call but using scan instead.

[pirj]

Thanks!

[JonRowe]

Released in 3.13.3