Enable liburing by default

[ibc]

Details

• Now that PR Update worker liburing dependency to 2.4-2 #1254 is merged (AKA new liburing wrap version with @jmillan's fix liburing: fix cc member check mesonbuild/wrapdb#1322) let's enable liburing again by default.
• ms_enable_liburing has been replaced with ms_disable_liburing (which of course is false by default).

Bonus tracks

• Add explicit --foreground-scripts to all npm ci commands in CI actions.
• Fix meson warning (fixes flatc warning: You should add the boolean check kwarg to the run_command call #1256).