Use a git-on-borg mirror for the Bindgen git repository

Bug: 1428298, 1426886
Change-Id: I1487f24dd40467552a18923547cb60805a885419
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4395903
Reviewed-by: Collin Baker <[email protected]>
Commit-Queue: danakj <[email protected]>
Cr-Commit-Position: refs/heads/main@{#1126030}
NOKEYCHECK=True
GitOrigin-RevId: 00c12debcb57d50a02c74d3fc97b5fd278360efb

Author: danakj

build_bindgen.py

@@ -30,8 +30,8 @@
 
 # The git hash to use. This is the `v0.60.0` tag.
 BINDGEN_GIT_VERSION = '355181134094202e0caae60c1fbf145d8e6ca84b'
-# TODO(crbug.com/1428298): Mirror to Git-on-Borg.
-BINDGEN_GIT_REPO = 'https://github.com/rust-lang/rust-bindgen'
+BINDGEN_GIT_REPO = ('https://chromium.googlesource.com/external/' +
+                    'github.com/rust-lang/rust-bindgen')
 
 BINDGEN_SRC_DIR = os.path.join(THIRD_PARTY_DIR, 'rust-toolchain-intermediate',
                                'bindgen-src')