x/build/cmd/watchflakes: misattributed test failures

[bcmills]

#60253 (comment) reported a number of failures in the golang.org/x/net/bpf package with summary lines suggesting that they were instead in the x/net/ipv6 package.

That caused them to be posted to the wrong issue (#60253 instead of #55235).

I suspect a watchflakes parser bug.

(attn @cherrymui)