deps: update dependency io.grpc:grpc-bom to v1.31.1 (#124)

This PR contains the following updates:

| Package | Update | Change |
|---|---|---|
| [io.grpc:grpc-bom](https://github.com/grpc/grpc-java) | patch | `1.31.0` -> `1.31.1` |

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### Release Notes

<details>
<summary>grpc/grpc-java</summary>

### [`v1.31.1`](https://github.com/grpc/grpc-java/releases/v1.31.1)

[Compare Source](https://github.com/grpc/grpc-java/compare/v1.31.0...v1.31.1)

Bug Fixes:

-   netty: The environment variable `GRPC_EXPERIMENTAL_AUTOFLOWCONTROL=false` will now disable the BDP monitoring introduced in v1.30.0. This is intended to help diagnose a “too_many_pings” compatibility issue and will be removed once it is resolved. If you need to use the variable, \_please_ file an issue
-   examples: some gRPC artifacts are missing in JCenter causing Android examples to sometimes fail to build. Now we are adding mavenCentral as fallback for the Android examples. See [#&#8203;5782](https://github.com/grpc/grpc-java/issues/5782)
-   xds: meshCA protocol buffers added in v1.31.0 are now properly shaded in an internal package
-   xds: fixed some internal breakage for traffic splitting

</details>

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pom.xml

@@ -55,7 +55,7 @@
     <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
     <site.installationModule>${project.artifactId}</site.installationModule>
 
-    <grpc.version>1.31.0</grpc.version>
+    <grpc.version>1.31.1</grpc.version>
     <gax.version>1.58.2</gax.version>
     <guava.version>29.0-android</guava.version>
     <protobuf.version>3.13.0</protobuf.version>