Incorrect configuration value name in unit tests

[Rarst]

The default test configuration in phpunit.xml.dist has threshold entry for slow tests that is incorrectly named.

The current config says <element key="slow_threshold"> and the name expected by code is slowThreshold.

While the code defaults to same 500ms value anyway, this is very confusing when config is edited or followed as an example and the new value doesn't apply.

[SergeyBiryukov]

Good catch! This was committed as slowThreshold in [35214], then switched to slow_threshold in [45607] per the coding standards.

Either the option name change should be reverted (I think the coding standards only apply to the variable name), or the option handling in SpeedTrapListener::loadOptions() should be changed too.

[SergeyBiryukov]

In 46881:

Tests: Correct the slowThreshold option name for SpeedTrapListener.

The previous change in [45607] appears to be accidental.

Props Rarst.
Fixes #48933.

[SergeyBiryukov]

Incidentally, the option name in tests/phpunit/multisite.xml​ was not altered in [45607] and is still correct.