Fix disk space checking on macOS hosts

[DL6ER]

What does this implement/fix?

Reintroduce a workaround for docker on macOS accidentally removed in bd266d6 and install proper safeguards around HTML escape code during message generation.

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Related issue or feature (if applicable): #1925

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

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[DL6ER]

Fixes #1925 - Bugfix confirmed by OP in said issue ticket

[DL6ER]

Fix confirmed working #1925 (comment)

[rdwebdesign]

Approved based on user confirmation.

Also, so far no one reported an issue with this branch.