[cr137] Fix checkout failure for build_rust_toolchain_aux

There was a failure when running `npm run build_rust_toolchain_aux` in
the CI, which wasn't reproducible locally, when fetching the tag. This
change fetches the tag straight from `googlesource` and this has worked
in the CI jobs.

Resolves https://github.com/brave/brave-browser/issues/45323

build/commands/scripts/buildRustToolchainAux.js

@@ -13,14 +13,13 @@ program
   .option('--tag <tag>', '(optional) A Chromium tag to be checked out for generating this toolchain.')
   .action((options) => {
     if (options.tag) {
-      tagRef = 'refs/tags/' + options.tag
-      util.runGit(config.srcDir, ['fetch', 'origin', tagRef + ':' + tagRef])
-      util.runGit(config.srcDir, ['reset', '--hard', tagRef])
+      util.runGit(config.srcDir, ['fetch', 'https://chromium.googlesource.com/chromium/src', 'tag', options.tag])
+      util.runGit(config.srcDir, ['reset', '--hard', options.tag])
 
       // Setting this env variable to prevent downloading the toolchain using
       // the new tag's revision, as the intent is to generate a new toolchain.
       process.env.SKIP_DOWNLOAD_RUST_TOOLCHAIN_AUX = '1'
-      util.runGClient(['sync', '--reset', '--upstream', '--revision', 'src@' + tagRef])
+      util.runGClient(['sync', '--reset', '--upstream', '--revision', 'src@refs/tags/' + options.tag])
     }
     args = [path.join(config.srcDir, 'brave', 'build', 'rust', 'build_rust_toolchain_aux.py')]
     if (options.out_dir) {