Update Rust crate base64 to 0.21.5

[renovate[bot]]

This PR contains the following updates:

Package	Type	Update	Change
base64	dependencies	patch	0.21.4 -> 0.21.5

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Release Notes

marshallpierce/rust-base64 (base64)

### [`v0.21.5`](https://togithub.com/marshallpierce/rust-base64/blob/HEAD/RELEASE-NOTES.md#0215) [Compare Source](https://togithub.com/marshallpierce/rust-base64/compare/v0.21.4...v0.21.5) - Add `Debug` and `Clone` impls for the general purpose Engine

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