[LTP] thermal: add new test group

[Petr Vorel]

Hi all,

actually v20 is better than this v21 => setting it changes requested.
I'd prefer to merge v20.

> Hi Piotr,

> On Thu, 14 May 2026 15:34:47 +0200, Piotr Kubaj wrote:
> > thermal: add new test group

> > +	while (sleep_time > 0) {
> > +		...
> > +		if (temp > temp_high)
> > +			break;
> > +		sleep(sleep_time--);

> G2: sleep() used for synchronization. This is not a timer API test so
> the G2 exemption does not apply. Consider polling with
> tst_timer_expired_ms() or discuss with maintainers if a thermal-specific
> exception is appropriate.

> > +			tst_res(TINFO, "Cooling down for %d seconds", COOLDOWN);
> > +			sleep(COOLDOWN);

> G2: Same issue — sleep() used as a synchronization barrier for CPU
> cooldown between zone tests. If a non-sleep alternative is genuinely
> infeasible for thermal testing, this needs explicit justification in the
> commit message.

Yes, cooldown could have been mentioned in the commit message, I'll add it for
v20.

Kind regards,
Petr