update CI workflows to only use pull_request event

[dariuszkuc]

Updating federation compatibility check to trigger on pull_request and use regular GITHUB_TOKEN. This eliminates potential security vulnerability on workflows triggered through pull_request_target event but has a drawback that comments from compatibility action will only work on PRs from origin (i.e. it will no longer be able to comment on PRs from forks).

[dariuszkuc]

Apollo Federation Subgraph Compatibility Results

Federation 1 Support	Federation 2 Support
_service 🟢 @key (single) 🟢 @key (multi) 🟢 @key (composite) 🟢 repeatable @key 🟢 @requires 🟢 @provides 🟢 federated tracing 🟢	@link 🟢 @shareable 🟢 @tag 🟢 @override 🟢 @inaccessible 🟢 @composeDirective 🟢 @interfaceObject 🟢

Learn more:

• Apollo Federation Subgraph Specification
• Compatibility Tests