rustPlatform.importCargoLock: download crates from static.crates.io

The crates.io API server's 1 req/sec rate limit currently surfaces as
intermittent HTTP 403 errors when vendoring lockfiles. Switch to the CDN
endpoint as recommended by upstream (rust-lang/crates.io#13482), mirroring
the fix already applied to fetchCargoVendor in #512735.

fetchurl is content-addressed by sha256, so the URL change does not affect
any downstream store paths.

Fixes #524979

pkgs/build-support/rust/import-cargo-lock.nix

@@ -130,7 +130,10 @@ let
     };
 
   registries = {
-    "https://github.com/rust-lang/crates.io-index" = "https://crates.io/api/v1/crates";
+    # Use static.crates.io (CDN) instead of crates.io/api to avoid the 1 req/sec
+    # rate limit on the API servers, which currently returns intermittent 403s.
+    # See https://github.com/rust-lang/crates.io/issues/13482
+    "https://github.com/rust-lang/crates.io-index" = "https://static.crates.io/crates";
   }
   // extraRegistries;