fix(deps): update dependency google-protobuf to ^3.21.4

[renovate]

This PR contains the following updates:

Package	Change	Age	Adoption	Passing	Confidence
google-protobuf	^3.20.1 -> ^3.21.4
@types/google-protobuf (source)	3.15.6 -> 3.15.12

Test plan: CI should pass with updated dependencies. No review required: this is an automated dependency update PR.

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Release Notes

protocolbuffers/protobuf-javascript (google-protobuf)

v3.21.4

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Release to fix bazel build layering issue in 3.21.3.

v3.21.2

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This is a hotfix release for #​141

v3.21.1

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• Enable Closure's advanced optimization mode by default. This should reduce code size (#​124).
• Replace goog.testing.asserts in tests with Jasmine expectations (#​136).
• Bring in the subset of the goog.asserts we use as jspb.asserts. This code retains an Apache 2.0 license.
• Fix decoding of signed varint32s (#​31).
• Add license files to NPM package.

This will also be our first release to have cross-compiled protoc-gen-js binaries. Please note that they use dynamic linking (similar to the protobuf protoc releases).

v3.21.0

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First release of protobuf-javascript as a standalone project.

This release mostly consists of BUILD and documentation fixes to account for new repository.
Various bug fixes.

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