deps: update dependency com.google.cloud:google-cloud-spanner-bom to v6.76.0

[renovate-bot]

This PR contains the following updates:

Package	Change	Age	Adoption	Passing	Confidence
com.google.cloud:google-cloud-spanner-bom	6.74.1 -> 6.76.0

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Warning

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Release Notes

googleapis/java-spanner (com.google.cloud:google-cloud-spanner-bom)

v6.76.0

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Features

• Add opt-in flag and ClientInterceptor to propagate trace context for Spanner end to end tracing (#​3162) (0b7fdaf)
• Add samples for backup schedule feature APIs. (#​3339) (8cd5163)

Bug Fixes

• deps: Update the Java code generator (gapic-generator-java) to 2.46.1 (1719f44)

v6.75.0

Compare Source

Features

• Support multiplexed session for blind write with single use transaction (#​3229) (b3e2b0f)

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