Bug 1865522 - Mark cargo clippy as requiring export. r=firefox-build-system-reviewers,sylvestre,ahochheiden

It needs .cargo/config from the objdir, which export creates.

Differential Revision: https://phabricator.services.mozilla.com/D194156

build/cargo/cargo-clippy.yaml

@@ -1,4 +1,5 @@
 ---
 command: cargo-clippy
 continue_on_error: true
+requires_export: true
 # cargo_build_flags: []