PR checks: Add a bundle URL input parameter for workflow dispatch events

[adityasharad]

The pr-checks.yml workflow has a workflow_dispatch event trigger so that we can run it manually. It is often useful to run manually and specify a URL to a particular CodeQL bundle, so we can test against it without having to modify defaults.json or the workflow itself.

I suggest adding a bundle URL parameter to the workflow_dispatch event. If that's available, include the URL in the list of tools values that are produced by the check-codeql-versions job. Currently it's [null, latest, <nightly URL>].