Additional func to retrieve default branch of an org/repo

[deepsm007]

Changes:

• Added a new createOrUpdatePROnDefaultBranch function to fetch a repo's default branch and update the PR
• Added unit tests to cover both success and error cases.

[k8s-ci-robot]

Hi @deepsm007. Thanks for your PR.

I'm waiting for a kubernetes-sigs member to verify that this patch is reasonable to test. If it is, they should reply with /ok-to-test on its own line. Until that is done, I will not automatically test new commits in this PR, but the usual testing commands by org members will still work. Regular contributors should join the org to skip this step.

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[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is NOT APPROVED

This pull-request has been approved by: deepsm007
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[petr-muller]

/ok-to-test

[k8s-ci-robot]

@deepsm007: The following tests failed, say /retest to rerun all failed tests or /retest-required to rerun all mandatory failed tests:

Test name	Commit	Details	Required	Rerun command
pull-prow-unit-test-race-detector-nonblocking	3bea76d	link	false	/test pull-prow-unit-test-race-detector-nonblocking
pull-prow-unit-test	3bea76d	link	true	/test pull-prow-unit-test
pull-prow-verify-lint	3bea76d	link	true	/test pull-prow-verify-lint
pull-prow-integration	3bea76d	link	true	/test pull-prow-integration

Full PR test history. Your PR dashboard. Please help us cut down on flakes by linking to an open issue when you hit one in your PR.

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[smg247]

I would stop trying to use the fakegithubclient for the purpose of this unit test. If you follow this example to define a new interface in bumper for only the ghc methods it actually needs then you can just mock those methods with a fake client of your own. They have done this exact thing in branchprotector.