Test for bfcache compatibility incorrectly flags use of no-cache and max-age=0

[westonruter]

The bfcache Site Health test (#1692 fixed via #1807) is currently checking for no-cache and max-age=0 when in reality it shouldn't be.

From Back/forward cache on Web.dev:

For pages that need to always serve up-to-date content—and that content does not contain sensitive information—use Cache-Control: no-cache or Cache-Control: max-age=0. These directives instruct the browser to revalidate the content before serving it, and they don't affect a page's bfcache eligibility.

Note that when a page is restored from bfcache, it is restored from memory, not from the HTTP cache. As a result, directives like Cache-Control: no-cache or Cache-Control: max-age=0 are not taken into account, and no revalidation occurs before the content is displayed to the user.

This article from Nitropack:

3. Use Cache-Control: no-store only with information-sensitive pages

If a page contains sensitive information and caching is inappropriate, then Cache-Control: no-store should be used to prevent it from being eligible for bfcache. On the other hand, if a page doesn't contain sensitive information and always requires up-to-date content, Cache-Control: no-cache or Cache-Control: max-age=0 can be used. These directives prompt the browser to revalidate the content before serving it and don't impact a page's eligibility for bfcache.

And in Monitoring bfcache blocking reasons on MDN, the only blocking reason for Cache-Control is the no-store directive:

"response-cache-control-no-store"

The page uses no-store as a Cache-Control header value.

And the Lighthouse audit strings:

https://github.com/GoogleChrome/lighthouse/blob/af88b935e3669601cef2d6adf7186a6624731446/core/lib/bf-cache-strings.js#L172-L175
https://github.com/GoogleChrome/lighthouse/blob/af88b935e3669601cef2d6adf7186a6624731446/core/lib/bf-cache-strings.js#L196-L200

Also, I tested serving pages with Cache-Control: no-cache, max-age=0 and the DevTools check showed it was successfully served from bfcache:

However, if I instead serve Cache-Control: no-store then I get a failure:

So the no-cache and max-age=0 checks should be removed from the test.

[westonruter]

Fixed by #1826