meson: silence warnings in rust subprojects

Rust 1.91 as well as clippy show various benign warnings in our dependencies. Silence them since we
can't really do much about them anyway and we want to enforce clippy complience via CI in the
future.

Matches cargo behavior, which also doesn't show warnings or clippy lints outside the workspace.

Reviewed-by: Eric Engestrom <eric@igalia.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/38814>

subprojects/packagefiles/rustc-hash-2-rs/meson.build

@@ -13,7 +13,7 @@ lib = static_library(
   'rustc_hash',
   'src/lib.rs',
   rust_args : rust_args,
-  override_options : ['rust_std=2021', 'build.rust_std=2021'],
+  override_options : ['rust_std=2021', 'build.rust_std=2021', 'warning_level=0'],
   rust_abi : 'rust',
 )