Rate Limit exceeded

[Lassulus]

We see an increase in 403 errors

NixOS/nixpkgs#348977 (comment)
NixOS/nixpkgs#349062 (comment)

which seems indicative of Rate Limiting.
From the GitHub docs:

If you exceed your primary rate limit, you will receive a 403 or 429 response, and the x-ratelimit-remaining header will be 0. You should not retry your request until after the time specified by the x-ratelimit-reset header.

If you exceed a secondary rate limit, you will receive a 403 or 429 response and an error message that indicates that you exceeded a secondary rate limit. If the retry-after response header is present, you should not retry your request until after that many seconds has elapsed. If the x-ratelimit-remaining header is 0, you should not retry your request until after the time, in UTC epoch seconds, specified by the x-ratelimit-reset header. Otherwise, wait for at least one minute before retrying. If your request continues to fail due to a secondary rate limit, wait for an exponentially increasing amount of time between retries, and throw an error after a specific number of retries.