Fix parsing of APIGENTOOLS_API_VERSION env variable

[jirikuncar]

What does this PR do?

Fixes parsing of APIGENTOOLS_API_VERSION environment variable. Currently, it would parse v1 as ("v", "1").

Description of the Change

Treats env value as : separated list.

Alternate Designs

n/a

Possible Drawbacks

n/a

Verification Process

APIGENTOOLS_API_VERSION=v1 apigentools config

Additional Notes

Release Notes

Review checklist (to be filled by reviewers)

• Feature or bug fix MUST have appropriate tests (unit, integration, etc...)
• PR title must be written as a CHANGELOG entry (see why)
• Files changes must correspond to the primary purpose of the PR as described in the title (small unrelated changes should have their own PR)
• PR must have one changelog/ label attached. If applicable it should have the backward-incompatible label attached.
• PR should not have do-not-merge/ label attached.
• If Applicable, issue must have kind/ and severity/ labels attached at least.