Make GDS workflow manual for PRs, automatic on main

[Copilot]

The GDS workflow consumes ~1 hour of CI time per run. To conserve the monthly actions quota, this changes the workflow to require manual triggering on PRs while maintaining automatic execution on the main branch.

Changes

• Added push trigger for main branch to run workflow automatically on merge
• Preserved manual PR behavior via existing run-gds label requirement
• Updated job condition to include push events: github.event_name == 'push'

Behavior

• PRs: Requires run-gds label (no change)
• Main branch: Runs automatically on every push (new)
• Manual trigger: workflow_dispatch still available (no change)

Original prompt

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This section details on the original issue you should resolve

<issue_title>Make GDS workflow manual</issue_title>
<issue_description>GDS workflow takes up a lot of time (about an hour right now) and thus eats at our monthly actions quota. To minimize the impact let's run it manual before merging the PR. </issue_description>

Comments on the Issue (you are @copilot in this section)

@TheDeepestSpace We need to make GDS workflow run automatically on main branch

• Fixes Make GDS workflow manual #8

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