Swap Valgrind for address-sanitizer/memory-sanitizer builds in CI

[saxbophone]

Valgrind is... super slow, and I'm a bit tired of waiting for my test suite to take 10 minutes to run...

[saxbophone]

https://stackoverflow.com/questions/47251533/memory-address-sanitizer-vs-valgrind

[saxbophone]

Hmmm, it seems you need to have the memory sanitizers installed. This may be more than just a five-minute thing...