RFR: 7903857: Include test run in GitHub Actions workflow [v2]

[Christian Stein]

> Please review this change to run APIDiff's self-tests for each pull request.

Christian Stein has updated the pull request incrementally with one additional commit since the last revision:

  Fix `/bin/sh: 2: set: Illegal option -o pipefail` error

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Changes:
  - all: https://git.openjdk.org/apidiff/pull/25/files
  - new: https://git.openjdk.org/apidiff/pull/25/files/f5ca7476..55a4f039

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=apidiff&pr=25&range=01
 - incr: https://webrevs.openjdk.org/?repo=apidiff&pr=25&range=00-01

  Stats: 1 line in 1 file changed: 0 ins; 1 del; 0 mod
  Patch: https://git.openjdk.org/apidiff/pull/25.diff
  Fetch: git fetch https://git.openjdk.org/apidiff.git pull/25/head:pull/25

PR: https://git.openjdk.org/apidiff/pull/25