Re-enable frame eval mode by default.

[fabioz]

It was disabled as temporary workaround in #346, but that was fixed and it appears it wasn't re-enabled...

[sonarcloud]

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[fabioz]

As a note, this change does seem to make the tests more prone to failure.

I tried analyzing those but I couldn't find out why that happens (it's possible that it's just timing differences in the test run).

It's weird that the failing tests appear to be some variation of:

2022-04-01T14:14:17.3234090Z   File "/Users/runner/work/1/s/.tox/py38/lib/python3.8/site-packages/debugpy/_vendored/pydevd/_pydevd_bundle/pydevd_comm.py", line 491, in start_client
2022-04-01T14:14:17.3234950Z     s.connect((host, port))
2022-04-01T14:14:17.3235520Z ConnectionRefusedError: [Errno 61] Connection refused

Meaning that the debugger is trying to connect to the client but it's not successful (and the change isn't related to that at all).

Also, failures seem to be tied mostly to MacOS.