Rust

Merge pull request #1387 from coreos/dependabot/cargo/base64-0.21.7 #2446

Job	Run time
Docs	1m 40s
Lints, pinned toolchain (x86_64)	1m 23s
Lints, pinned toolchain (s390x)	9m 9s
Tests, minimum supported toolchain (x86_64)	2m 45s
Tests, minimum supported toolchain (s390x)	14m 46s
Tests, unstable toolchain (beta, x86_64)	2m 35s
Tests, unstable toolchain (nightly, x86_64)	2m 31s
Tests, stable toolchain (x86_64)	2m 36s
Tests, stable toolchain (s390x)	14m 7s
	51m 32s

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