Fixed a few other flaky tests

[LorenzoBettini]

This should remove further flakyness

• QuickDebugSourceInstallingCompilationParticipantTest: in the end, it looks like the problem was that the generated .class Eclipse resource was not fully synchronized
• Some tests did not properly reset the autobuild state

[github-actions]

Test Results

  6 461 files  + 1 547    6 461 suites  +1 547   3h 20m 19s ⏱️ + 31m 39s
 43 241 tests ±     0   42 657 ✅ +     1    584 💤 ±  0  0 ❌ ±0 
170 051 runs  +42 003  167 714 ✅ +41 417  2 337 💤 +587  0 ❌ ±0 

Results for commit ec36fa2. ± Comparison against base commit 09af658.

[szarnekow]

Reasonable. Let’s try this