x/pkgsite: Search bar says "Search for a package" when symbol search is selected.

[prattmic]

What is the URL of the page with the issue?

https://beta.pkg.go.dev/gvisor.dev/gvisor/pkg/sentry/kernel

What is your user agent?

Mozilla/5.0 (X11; CrOS x86_64 13982.69.0) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/92.0.4515.130 Safari/537.36

Screenshot

What did you do?

Select "Symbols" in the search box. (I think it may have automatically been set to Symbols when I got to the page, but I don't quite remember.)

What did you expect to see?

Something like "Search for a symbol".

What did you see instead?

"Search for a package"

[gopherbot]

Change https://golang.org/cl/346090 mentions this issue: static: update search placeholder for symbol search