or the following, which might also not generate any overhead because the GDScript bytecode compiler could easily optimize it away (don't know if it does, though), and reads nicely:
move_and_slide(...) and "ignore return value"
or even this, which is very short, but rather cryptic:
move_and_slide(...) or false
exuins solution is probably best.
(BTW, with the above "and"/"or" options, you'll get another warning, "standalone expression"... so that might not be too useful; it's just a way to convert one warning into another one :-)