bug: update tests are making external web requests

Many of the TestUpdate tests are making external web requests to repo1 to check for updates. This is causing all tests to fail when cutting a new release that does not currently exist on the server (!22 (merged)).

Tests should always mock out external dependencies and under no circumstances make HTTP requests to external systems.

Acceptance Criteria

• Use the test HTTP server to mock out the expected responses from repo1
• Configure the update checker to ping the mocked out server instead of repo1 directly
• Tests should be able to run offline and need to work when the local version (https://repo1.dso.mil/big-bang/apps/developer-tools/bbctl/-/blob/main/static/resources/constants.yaml?ref_type=heads#L6) exceeds the declared versions in the test suite.