Use Cirrus credits for billing.

[kf6gpe]

Description

We've been on the free tier for cirrus billing on Windows and Linux. Migrate to billing against our PO.

No tests.

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/

[fkorotkov]

/cc @Hixie for #41880

[gspencergoog]

[kf6gpe]

Merging per face to face discussion with Greg, despite the broken build.