fix: skip dangerouslySetInnerHtml hydration warning if it's undefined (#18676)

* test: Add failing case for dangerouslySetInnerHtml=undefined

* fix: skip dangerouslySetInnerHtml warning if it's undefined

* test: add similar test that should trigger the warning

* chore: Remove redundant nullish check

* Poke yarn_test_www_variant which timed out

* test: Add smaller test for innerHTML=string to innerHTML=undefined