general: T8595: address Copilot review threads on test command and commit convention

• Line 15: add ansible-test units alongside the existing pytest command; the two correspond to the unit-galaxy and unit-source CI jobs respectively, so documenting both gives contributors accurate options for each CI path.

• Line 30: change "Commit / PR title" to "Commit headline". No workflow in this repo enforces PR title format; the PR template checklist confirms only commit headlines must carry a Phorge task ID.

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