fix(deps): Update dependency @grpc/grpc-js to v1.12.6 (#266)

This PR contains the following updates:

| Package | Type | Update | Change |
|---|---|---|---|
| [@grpc/grpc-js](https://grpc.io/) ([source](https://redirect.github.com/grpc/grpc-node)) | dependencies | patch | [`1.12.5` -> `1.12.6`](https://renovatebot.com/diffs/npm/@grpc%2fgrpc-js/1.12.5/1.12.6) |

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### Release Notes

<details>
<summary>grpc/grpc-node (@&#8203;grpc/grpc-js)</summary>

### [`v1.12.6`](https://redirect.github.com/grpc/grpc-node/releases/tag/%40grpc/grpc-js%401.12.6)

[Compare Source](https://redirect.github.com/grpc/grpc-node/compare/@grpc/grpc-js@1.12.5...@grpc/grpc-js@1.12.6)

-   Allow garbage collection of IDLE channels ([#&#8203;2896](https://redirect.github.com/grpc/grpc-node/issues/2896))

</details>

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