Add --sync src/tools/cargo/Cargo.toml for Rust toolchain cargo vendor

Upstream's nightly tarball maker has added this Cargo.toml file to its
list of sync targets, and we need to match.

R=zequanwu@google.com

Bug: 1441917
Change-Id: I8cfbda9a5cdb79a7d7f5c4b77748b99f4fd9561a
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4507181
Commit-Queue: danakj <danakj@chromium.org>
Reviewed-by: Zequan Wu <zequanwu@google.com>
Cr-Commit-Position: refs/heads/main@{#1139678}
NOKEYCHECK=True
GitOrigin-RevId: 11ac6084f6f9577bfdc761d7bdd483849b5298a7

Author: danakj

build_rust.py

@@ -270,7 +270,7 @@ def CargoVendor(cargo_bin):
         else:
             sys.exit(1)
 
-        # From https://github.com/rust-lang/rust/blob/master/src/bootstrap/dist.rs#L986-L995:
+        # From https://github.com/rust-lang/rust/blob/master/src/bootstrap/dist.rs#L1003-L1013:
         # The additional `--sync` Cargo.toml files are not part of the top level
         # workspace.
         vendor_cmd = [
@@ -279,6 +279,8 @@ def CargoVendor(cargo_bin):
             '--locked',
             '--versioned-dirs',
             '--sync',
+            'src/tools/cargo/Cargo.toml',
+            '--sync',
             'src/tools/rust-analyzer/Cargo.toml',
             '--sync',
             'compiler/rustc_codegen_cranelift/Cargo.toml',