Fix build of wgpu-hal on macOS with features = ["gles"]. (#7266)

Without this change, `cargo build -p wgpu-hal --features=gles` will fail
if `target_os = "macos"`.

wgpu-hal/Cargo.toml

@@ -112,6 +112,7 @@ gles = [
     "dep:libloading",
     "dep:log",
     "dep:ndk-sys",
+    "dep:objc",
     "dep:profiling",
     "dep:wasm-bindgen",
     "dep:web-sys",