This PR speeds up the "Upload tests to datadog" step by downloading the
`datadog-ci` binary directly from GitHub releases. Most of the time used
to be spent in `npm install`, which consistently timed out on Windows
after a minute. [Now it takes 3
seconds](https://github.com/coder/coder/actions/runs/14834976784/job/41644230049?pr=17668#step:10:1).
I updated it to version v2.48.0 because v2.21.0 didn't have the
artifacts for arm64 macOS.
Use specific commit SHAs for GitHub actions across various workflows to
enhance reliability and reproducibility. This change ensures that
actions run against a known version, reducing the risk of unexpected
issues due to updates in the third-party action repositories.
This contributes to improving the score in #14879
Dean Sheather