[CI] 4746 - Avoid extraneous CI runs (master)

[wileyj]

Small change to the ci workflow to reduce the frequency of when CI is triggered.
previously, various workflows would trigger:

• open a PR
• new commits to a PR
• PR approvals
• add PR to merge group
• would not trigger if only change is yml/md

This change does the following:

• workflow triggers when a PR:
  • is opened
  • is changed
  • only updated files are md/yml (this will be addressed in a future PR - today the required status checks would make this problematic)
• workflow no longer runs:
  • when PR is approved

[hstove]

Moment of truth - will it run when I approve?

[obycode]

Looks right to me!