Auto merge of #16487 - aneeshusa:automatically-clean-old-nightlies, r=larsbergstrom

Automatically clean old nightlies

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Automatically clean old rustc and cargo nightlies on our builders up to preserve disk space.

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- [ ] `./mach build -d` does not report any errors
- [x] `./mach test-tidy` does not report any errors
- [ ] These changes fix #12103 and help with servo/saltfs#321 (github issue number if applicable).

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- [ ] There are tests for these changes OR
- [x] These changes do not require tests because tested manually

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