lib/Kconfig.debug: fix grammar in RUST_BUILD_ASSERT_ALLOW

Just a grammar fix in lib/Kconfig.debug, under the config option
RUST_BUILD_ASSERT_ALLOW.

Reported-by: Miguel Ojeda <ojeda@kernel.org>
Closes: #1006
Fixes: ecaa6dd ("rust: add `build_error` crate")
Signed-off-by: Timo Grautstueck <timo.grautstueck@web.de>
Link: https://lore.kernel.org/r/20241006140244.5509-1-timo.grautstueck@web.de
Signed-off-by: Miguel Ojeda <ojeda@kernel.org>

lib/Kconfig.debug

@@ -3060,7 +3060,7 @@ config RUST_BUILD_ASSERT_ALLOW
 	bool "Allow unoptimized build-time assertions"
 	depends on RUST
 	help
-	  Controls how are `build_error!` and `build_assert!` handled during build.
+	  Controls how `build_error!` and `build_assert!` are handled during the build.
 
 	  If calls to them exist in the binary, it may indicate a violated invariant
 	  or that the optimizer failed to verify the invariant during compilation.