Run all tests in release build in long suite on master merge

[derekbruening]

Historically we've been focused on debug-build tests, under the assmption that it is pretty rare for an issue to happen only in release build. Debug build has extra checks that catch more errors. Today we run only a subset of tests in release build, based on that assumption and to keep the PR CI time down. But: we have a separate "long" suite on master merge where the time doesn't matter as much. We should enable all the tests in release-build there.

This is becoming more important as we have lately been seeing release-build-only failures: #4928, #4954, #2417 drcachesim.coherence.

[derekbruening]

Xref #4800, #1807

[derekbruening]

For the long suite x86_64 today we're running just over half the tests in release vs debug:

debug-internal-64: 791 tests passed, **** 7 tests failed, of which 2 were flaky, but ignoring 5 for i#2941: ****
release-external-64: all 397 tests passed