Run top-level build jobs in CI with python3
Description
This PR modifies the top-level build jobs in the CI pipeline to use python3.
API Changes and Justification
Backwards Compatible Changes
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This change introduces no API changes -
This change adds new API calls
Backwards Incompatible Changes
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This change modifies an existing API -
This change removes an existing API
If any of the Backwards Incompatible check boxes are ticked please provide a justification why this change is necessary and why it needs to be done in a backwards incompatible way.
Review Status
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