Limit docker label to linux special.system

[sophia-guo]

Related adoptium/temurin-build#4025

[github-actions]

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[smlambert]

Adding a comment for future consideration only, does not block merging this PR.

[smlambert]

Wondering if this adversely affects others using our pipelines (this is specific to Temurin (Eclipse Adoptium 'vendor' specific). Since no one has complained about this already, I will assume no, but future enhancement would be to frame it to only affect if vendor == Eclipse Adoptium).

[sophia-guo]

Updated with buildConfig.VARIANT == 'temurin' with comment.