[8.1](backport #30781) ci: split windows in mandatory and ext_win stages

[mergify]

This is an automatic backport of pull request #30781 done by Mergify.

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[elasticmachine]

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• Start Time: 2022-03-15T08:44:21.865+0000

• Duration: 213 min 57 sec

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Test	Results
Failed	0
Passed	27933
Skipped	2399
Total	30332

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