fix outdated URLs in readme docs of code generation scripts

Author: rhysd

scripts/generate-availability/README.md

@@ -5,7 +5,7 @@ This is a script for generating [`availability.go`](../../availability.go).
 
 It does:
 
-1. Fetch [the official contexts document](https://github.com/github/docs/blob/main/content/actions/learn-github-actions/contexts.md)
+1. Fetch [the official contexts document](https://raw.githubusercontent.com/github/docs/main/content/actions/writing-workflows/choosing-what-your-workflow-does/accessing-contextual-information-about-workflow-runs.md)
 2. Parse the markdown file and find "Context availability" table
 3. Extract contexts and special functions from the table
 4. Generate Go function and variable to map from workflow keys to available contexts and special functions

scripts/generate-webhook-events/README.md

@@ -5,7 +5,7 @@ This is a script for generating [`all_webhooks.go`](../../all_webhooks.go).
 
 It does:
 
-1. Fetch [the official markdown document](https://raw.githubusercontent.com/github/docs/main/content/actions/using-workflows/events-that-trigger-workflows.md)
+1. Fetch [the official markdown document](https://raw.githubusercontent.com/github/docs/main/content/actions/writing-workflows/choosing-when-your-workflow-runs/events-that-trigger-workflows.md)
 2. Parse the markdown file and find Webhook names and their types from tables
 3. Generate mappings from Webhook names to their types as Go map variable