Was that the PrimeGrid homepage or some other page? If it was a forum page, I found references to that warning going back several years. What happens is that sometimes Google, for whatever reason, rightly or wrongly flags some common website that people are using in their signature, and whenever you view a forum thread that includes a post by any user with that URL in their signature, you get that warning from google.
In one instance, the erroneous URL was that of CPU-Z, and people on tech forums were getting that warning left and right.
valid.canardpc.com is the CPU-Z validation site. Whether it actually has been infected with malware or not, what's happening here is that somebody's signature links to that site (showing off their computer's details), and that's triggering the warning.
There's nothing to worry about when browsing PrimeGrid.
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