ci: Lock Intel GPU frequency for performance tests
In order to ensure consistent results when running performance tests, it's necessary to lock the frequency for Intel GPUs to a fixed value.
Let's try with 70% of the maximum allowed by hardware. According to the initial research and testing, this seems to offer a good balance between execution speed and performance results consistency.
Also note that an increase of the frequency will also rise the rate of throttling events, with a negative impact on consistency. We can monitor such events in the logs, as in the following example:
GPU throttling detected: act=200 min=850 cur=850 RPn=100
This shows that the actual GPU frequency was 200 MHz, which is much lower than the required minimum of 850 MHz.