fix: determine if the branch exists first

[dcshzj]

Problem

We get a lot of such errors when users access their site dashboard when retrieving the last saved and last published information:

Error when getting latest commit of "master" branch: Error: fatal: ambiguous argument 'master': unknown revision or path not in the working tree.

This happens because we try to get the Git log for the master branch first, before attempting on origin/master. The first one will fail as the master branch does not exist on EFS, but origin/master does.

Solution

Breaking Changes

• Yes - this PR contains breaking changes
• No - this PR is backwards compatible with ALL of the following feature flags in this doc

Bug Fixes:

• Determine if the branch exists first before continuing to get the Git log, so that we avoid encountering the error unnecessarily.

Tests

• Navigate to any site dashboard.
• Verify from the logs that there are no errors shown that matches the error log above.
• Verify that you can see Unable to ascertain that "master" branch... log line as an info log.

Deploy Notes

None

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