Set eclipse-test-plugin packaging for saveparticipant tests

[HannesWell]

Contributes to

• Baseline comparision failes for tests removed from Eclipse P2-repository eclipse.platform.releng.aggregator#3784

[github-actions]

Test Results

    51 files   - 3      51 suites   - 3   33m 26s ⏱️ - 1m 52s
 4 555 tests  - 3   4 533 ✅  - 3   22 💤 ±0  0 ❌ ±0 
12 261 runs   - 9  12 105 ✅  - 9  156 💤 ±0  0 ❌ ±0 

Results for commit 8c4a939. ± Comparison against base commit 441ec40.

This pull request removes 3 tests.

org.eclipse.core.tests.resources.saveparticipant.SaveManagerTest ‑ test1
org.eclipse.core.tests.resources.saveparticipant.SaveManagerTest ‑ test2
org.eclipse.core.tests.resources.saveparticipant.SaveManagerTest ‑ test3

[HannesWell]

Verification builds cannot pass due to the linked issue.