ci: use a smarter `git status` check for uncommitted files

[jiridanek]

Description

This is stolen from a recent kubeflow PR by @ederign. Compared to the previous version, this also reports on new untracked files. Also, the command is much simpler to read.

How Has This Been Tested?

See GHA results.

Merge criteria:

• [x] The commits are squashed in a cohesive manner and have meaningful messages.
• [x] Testing instructions have been added in the PR body (for PRs involving changes that are not immediately obvious).
• [x] The developer has manually tested the changes and verified that the changes work

[openshift-ci[bot]]

[APPROVALNOTIFIER] This PR is APPROVED

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This pull-request has been approved by: caponetto

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