RFR: 7903836: apidiff: Add GitHub Actions test workflow

[Jonathan Gibbons]

On Wed, 25 Sep 2024 15:56:16 GMT, Christian Stein <cstein at openjdk.org> wrote:

> Please review this test workflow for building ApiDiff on every pull request.

"Provisional" approval, to enable the workflow

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Marked as reviewed by jjg (Reviewer).

PR Review: https://git.openjdk.org/apidiff/pull/9#pullrequestreview-2328775629