Site Health: Add site environment type to the debug information.

Follow-up to [47919], [48188], [48372].

Props joostdevalk, Clorith.
Merges [48802] to the 5.5 branch.
Fixes #50887.
Built from https://develop.svn.wordpress.org/branches/5.5@48805


git-svn-id: https://core.svn.wordpress.org/branches/5.5@48567 1a063a9b-81f0-0310-95a4-ce76da25c4cd