fix(deps): update rust crate base64 to 0.22

[renovate]

This PR contains the following updates:

Package	Type	Update	Change	OpenSSF
base64	dependencies	minor	0.21 -> 0.22

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Release Notes

marshallpierce/rust-base64 (base64)

v0.22.0

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• DecodeSliceError::OutputSliceTooSmall is now conservative rather than precise. That is, the error will only occur if the decoded output cannot fit, meaning that Engine::decode_slice can now be used with exactly-sized output slices. As part of this, Engine::internal_decode now returns DecodeSliceError instead of DecodeError, but that is not expected to affect any external callers.
• DecodeError::InvalidLength now refers specifically to the number of valid symbols being invalid (i.e. len % 4 == 1), rather than just the number of input bytes. This avoids confusing scenarios when based on interpretation you could make a case for either InvalidLength or InvalidByte being appropriate.
• Decoding is somewhat faster (5-10%)

v0.21.7

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• Support getting an alphabet's contents as a str via Alphabet::as_str()

v0.21.6

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• Improved introductory documentation and example

v0.21.5

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• Add Debug and Clone impls for the general purpose Engine

v0.21.4

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• Make encoded_len const, allowing the creation of arrays sized to encode compile-time-known data lengths

v0.21.3

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• Implement source instead of cause on Error types
• Roll back MSRV to 1.48.0 so Debian can continue to live in a time warp
• Slightly faster chunked encoding for short inputs
• Decrease binary size

v0.21.2

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• Rollback MSRV to 1.57.0 -- only dev dependencies need 1.60, not the main code

v0.21.1

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• Remove the possibility of panicking during decoded length calculations
• DecoderReader no longer sometimes erroneously ignores
  padding #​226

Breaking changes

• Engine.internal_decode return type changed
• Update MSRV to 1.60.0

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