chore(deps): update dependency com_google_protobuf to v3.15.4 (#632)
chore(deps): update dependency com_google_protobuf to v3.15.4 (#632)

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This PR contains the following updates:

| Package | Type | Update | Change |
|---|---|---|---|
| [com_google_protobuf](https://togithub.com/protocolbuffers/protobuf) | http_archive | patch | `v3.15.3` -> `v3.15.4` |

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### Release Notes

<details>
<summary>protocolbuffers/protobuf</summary>

### [`v3.15.4`](https://togithub.com/protocolbuffers/protobuf/releases/v3.15.4)

[Compare Source](https://togithub.com/protocolbuffers/protobuf/compare/v3.15.3...v3.15.4)

### Ruby

-   Fixed SEGV when users pass nil messages ([#&#8203;8363](https://togithub.com/protocolbuffers/protobuf/issues/8363))
-   Fixed quadratic memory usage when appending to arrays ([#&#8203;8364](https://togithub.com/protocolbuffers/protobuf/issues/8364))

### C++

-   Create a CMake option to control whether or not RTTI is enabled ([#&#8203;8361](https://togithub.com/protocolbuffers/protobuf/issues/8361))

### PHP

-   read_property() handler is not supposed to return NULL ([#&#8203;8362](https://togithub.com/protocolbuffers/protobuf/issues/8362))

</details>

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