Tweaks to ad load time testing

[emma-imber]

What does this change?

Adds 10 more articles to be tested for ad load speed. Also round the final figure we show for load time to avoid long recurring decimals being outputted.

Why?

Adding a few more articles should improve the reliability of the testing but it doesn't speed it up dramatically - it still runs in less than 3 minutes. Looping through the articles we already had slowed things down a lot more. Plus I think having a wider variety of articles let's us balance out differences between them to be more representative of what's on the site.

Reliability

I've run the check using 30 articles 12 times. These are the consented results I saw:

4474
4486
4488
4488
4494
4500
4502
4506
4570
4659
4698
5453

The median value is 4501 ms and the interquartile range is 126.5

There's one big outlier of 5453 ms, but otherwise the results weren't miles away from each other

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Latest commit: 927350a

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[github-actions]

Ad load time test results

For consented, top-above-nav took on average 4486ms to load.
For consentless, top-above-nav took on average 3199ms to load.

Test conditions:

• 5mbps download speed
• 1.5mbps upload speed
• 150ms latency