Fix: Update tox.ini for tox v4.0+

Fix: Update tox.ini for tox v4.0+

There are a couple of changes in tox v4.0+ not compatible with tox.ini.

The 'whitelist_externals' key was removed. Use 'allowlist_externals'
instead.

'passenv' does not support a space-separated list any more.
Use a comma-separated list instead. Also, remove duplicate environment
variables since the names are not case sensitive.

https://tox.wiki/en/4.4.11/upgrading.html#upgrading
https://tox.wiki/en/4.4.11/config.html#passenv

Change-Id: I188cc4ea20d187e44a7a2a7f07845306dd4b81fe
Signed-off-by: Sangwook Ha <[email protected]>