build: Bump Meson dependency to 0.50
build: Bump Meson dependency to 0.50

This shuts up an unhelpful warning about using
“install arg in configure_file”. It’s unhelpful because it’s in the
tests, dealing with installed tests, so has almost no bearing on whether
the library can be built successfully for 90% of people.

Signed-off-by: Philip Withnall <12d956b70be7f0d60e54e48e97a01dac38dce989@endlessos.org>

pwithnall/walbottle