CASSANDRA-20178: Make SetGetCompactionThroughputTest locale-agnostic

[Rajneesh180]

The test SetGetCompactionThroughputTest fails on locales that use a comma (,) as a decimal separator (like de_DE). This PR makes the regex pattern locale-agnostic by using [.,] for decimals.

patch by Rajneesh180; reviewed by TBD for CASSANDRA-20178

[Rajneesh180]

Hi @smiklosovic,

This is a one-line fix for CASSANDRA-20178 — the SetGetCompactionThroughputTest regex was doing a literal . match for the decimal separator, which fails on locales that use a comma (e.g. de_DE). Changed to [.,] to make it locale-agnostic.

No logic change, just a regex correction. Happy to adjust if there's a preferred pattern for locale handling in the test suite.