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

[Christian Stein]

> Please review this change to actually run ApiDiff's self-tests on all three major platforms.

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

  Remove `set -o pipefail` from test run

-------------

Changes:
  - all: https://git.openjdk.org/apidiff/pull/23/files
  - new: https://git.openjdk.org/apidiff/pull/23/files/49fd0e55..f68c3e3c

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=apidiff&pr=23&range=01
 - incr: https://webrevs.openjdk.org/?repo=apidiff&pr=23&range=00-01

  Stats: 2 lines in 1 file changed: 0 ins; 1 del; 1 mod
  Patch: https://git.openjdk.org/apidiff/pull/23.diff
  Fetch: git fetch https://git.openjdk.org/apidiff.git pull/23/head:pull/23

PR: https://git.openjdk.org/apidiff/pull/23