Append no_fqdn_available when no local suffix has been defined

[DL6ER]

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See title. The behavior we are improving here has not been released to master, so far.
This PR, together with pi-hole/docs#578, fixes #1205.

[DL6ER]

It's again the GHA tests that are failing. @PromoFaux Looking at, e.g., https://github.com/pi-hole/FTL/pull/1209/checks?check_run_id=3835806890

Expected:

# dns_queries_today 80

Found:

# dns_queries_today 72

Looking at what we have here, we see a lot of replies are not answered by 8.8.8.8#53. This is strange as Google's DNS turned out to be, by far (!), the most reliable DNS server out there. Either the GHA have a very bad connection to them (I don't believe this) or other jobs running on the same IP block may be able to trigger rate-limiting on their servers?