[4.0] Make sure hsts is only added on https sites

[zero-24]

Pull Request for Issue #30886

Summary of Changes

Make sure hsts is only added on https sites

Testing Instructions

• install 4.x on a http site (localhost for example)
• enable hsts from the plugin
• notice it is added to the header
• apply this patch
• see its gone
• install this patch on a https site
• make sure the hsts header is still added

Actual result BEFORE applying this Pull Request

HSTS is added on http sites

Expected result AFTER applying this Pull Request

HSTS is only added on https site.

Documentation Changes Required

None

[richard67]

I have tested this item ✅ successfully on 48eee3b

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[hans2103]

I have tested this item ✅ successfully on 48eee3b

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_{This comment was created with the J!Tracker Application at issues.joomla.org/tracker/joomla-cms/30902.}

[Quy]

RTC

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_{This comment was created with the J!Tracker Application at issues.joomla.org/tracker/joomla-cms/30902.}

[HLeithner]

thanks