Add recipients for GitHub API alerts

[zxiiro]

Forgot to add receipients for the GitHub API alerts.

[Copilot]

Pull Request Overview

This PR adds notification recipients for GitHub API rate limit alerts that were previously missing. The change ensures proper alerting when GitHub API rate limits are exceeded.

• Adds Slack and webhook notification recipients to an existing GitHub API alert

[github-actions]

OpenTofu plan for prod

Plan: 0 to add, 1 to change, 0 to destroy.

OpenTofu used the selected providers to generate the following execution
plan. Resource actions are indicated with the following symbols:
!~  update in-place

OpenTofu will perform the following actions:

  # datadog_monitor.GitHub_API_usage_unusually_high will be updated in-place
!~  resource "datadog_monitor" "GitHub_API_usage_unusually_high" {
        id                   = "9357250"
!~      message              = <<-EOT
            # GitHub API usage is unusually high
            
            We've detected that the GitHub API rate limit usage is higher than usual. This could be an indication of a problem in the ALI system causing higher than expected API calls.
            
            ## Action
            
            Review the rate limit metrics as well as API call count from the ALI for each API call to see if anything unusual is occurring.
          + 
          + @slack-PyTorch-pytorch-infra-alerts
          + @slack-Linux_Foundation-pytorch-alerts
          + @webhook-lf-incident-io
        EOT
        name                 = "GitHub API usage unusually high"
        tags                 = []
#        (15 unchanged attributes hidden)

#        (1 unchanged block hidden)
    }

Plan: 0 to add, 1 to change, 0 to destroy.

✅ Plan applied in Tofu Apply #14