I don't think this is from Google. Note how the from address is "via" something? None of the official Google Security Alerts I have received have that.
Does it actually show DKIM failing in the headers? I find it hard to believe that Google would allow their DKIM to be misconfigured, and if they did there would be thousands of people experiencing this behavior and posting about it.
What does that via say? That looks like it was forwarded or something. IDK, it looks like Google correctly identified something fishy about that email, and they don’t exempt their own emails from the rules (which is good).