Fix parsing of envvars with more than one =

[DL6ER]

What does this implement/fix?

Ensure we do not split too often at '=' while processing environment variables. This is an issue with multiple = being present in environment variables.

---

Related issue or feature (if applicable): N/A

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

---

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:

• The code change is tested and works locally.
• I based my code and PRs against the repositories developmental branch.
• I signed off all commits. Pi-hole enforces the DCO for all contributions
• I signed all my commits. Pi-hole requires signatures to verify authorship
• 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/v6-post-release-fixes-and-findings/76480/1