Fix spurious "resource limit exceeded" messages (v5 backport)

[DL6ER]

What does this implement/fix?

Backports https://github.com/pi-hole/FTL/pull/1892 to FTL v5.25 - aiming straight for a bugfix release.

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Related issue or feature (if applicable): https://discourse.pi-hole.net/t/pihole-unbound-dnsmasq-validation-failed-resource-limit-exeeded/68388

Pull request in docs with documentation (if applicable): N/A

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By submitting this pull request, I confirm the following:

1. I have read and understood the contributors guide, as well as this entire template. I understand which branch to base my commits and Pull Requests against.
2. I have commented my proposed changes within the code.
3. I am willing to help maintain this change if there are issues with it later.
4. It is compatible with the EUPL 1.2 license
5. I have squashed any insignificant commits. (git rebase)

Checklist:

• [x] The code change is tested and works locally.
• [x] I based my code and PRs against the repositories developmental branch.
• [x] I signed off all commits. Pi-hole enforces the DCO for all contributions
• [x] I signed all my commits. Pi-hole requires signatures to verify authorship
• [x] I have read the above and my PR is ready for review.

[pralor-bot]

This pull request has been mentioned on Pi-hole Userspace. There might be relevant details there:

https://discourse.pi-hole.net/t/pihole-unbound-dnsmasq-validation-failed-resource-limit-exeeded/68388/27

[DL6ER]

Confirmed on Discourse:

I was able to reproduce the error every time and can confirm that it no longer occurs with this version.