Support new buildifier release naming for linux_amd64 (#2449)

The CI script fails when attempting to download any buildifier version
because the releases asset content does not match buildifier or
buildifier-linux-amd64.
Make the get_release_url method support the new buildifier-linux_amd64
asset name associated with v8.5.1:

```
Downloading Buildifier version '8.2.1'
--
🛠️ Printing raw output for debugging
##### :bazel: buildifier: error while downloading Buildifier:
<pre><code>There is no Buildifier binary for release v8.5.1</code></pre>
 
See [job 019c0b2b-ffb9-45eb-9d73-e7ae090afe54](#019c0b2b-ffb9-45eb-9d73-e7ae090afe54)
```
Observed here:
https://buildkite.com/bazel/buildfarm-farmer/builds/12533/steps/canvas?sid=019c0b2b-ff6c-4bab-9425-336368855db4