fix(deps): update dependency io.grpc:grpc-bom to v1.68.2

[renovate[bot]]

This PR contains the following updates:

Package	Change	Age	Adoption	Passing	Confidence
io.grpc:grpc-bom	1.68.1 -> 1.68.2

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Release Notes

grpc/grpc-java (io.grpc:grpc-bom)

### [`v1.68.2`](https://redirect.github.com/grpc/grpc-java/releases/tag/v1.68.2) [Compare Source](https://redirect.github.com/grpc/grpc-java/compare/v1.68.1...v1.68.2) #### Bug Fixes - api: When forwarding from Listener onAddresses to Listener2 continue to use onResult ([https://github.com/grpc/grpc-java/pull/11688](https://redirect.github.com/grpc/grpc-java/pull/11688)). This fixes a 1.68.1 "IllegalStateException: Not called from the SynchronizationContext" regression ([#​11662](https://redirect.github.com/grpc/grpc-java/issues/11662)) that could be seen in certain custom NameResolvers - okhttp: If the frame handler thread is null do not schedule it on the executor ([https://github.com/grpc/grpc-java/pull/11716](https://redirect.github.com/grpc/grpc-java/pull/11716)). This fixes a 1.68.1 NullPointerException regression when a custom transportExecutor was provided to the channel and it did not have enough threads to run new tasks #### Improvements - examples: Use xds-enabled server and xds credentials in example-gcp-csm-observability ([https://github.com/grpc/grpc-java/pull/11707](https://redirect.github.com/grpc/grpc-java/pull/11707))

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