acc: Shrink the regression report comment

[denik]

Follow-up to #7105. The comments on #6989 and #7109 were 34-44 KB, close to the 60 KB cap, mostly because a new test fails the same way on main and on the latest release and the same diff was printed twice.

• A failing run whose output equals an earlier column's (ignoring the random temp dir) now says "same output as ".
• When the comment is over the cap, whole failure details are dropped (with a count) instead of cutting one in the middle and leaving its markup open.

This pull request and its description were written by Isaac.

[eng-dev-ecosystem-bot]

Integration test report

Commit: 482e90f

Run: 39433941397

	Env	✅​pass	🙈​skip	Time
✅​	aws linux-2core-8gb	281	15	4:34
✅​	aws-windows-latest-4core-16gb	283	13	4:05
✅​	azure linux-2core-8gb	280	15	4:16
✅​	azure-windows-latest-4core-16gb	282	13	3:42
✅​	gcp linux-2core-8gb	281	15	4:34
✅​	gcp-windows-latest-4core-16gb	283	13	4:10

Top 3 slowest tests (at least 2 minutes):

duration	env	testname
4:04	gcp-windows-latest-4core-16gb	TestAccept
4:01	aws-windows-latest-4core-16gb	TestAccept
3:35	azure-windows-latest-4core-16gb	TestAccept