deps: update dependency com.google.cloud:google-cloud-spanner-bom to v6.57.0

[renovate-bot]

This PR contains the following updates:

Package	Change	Age	Adoption	Passing	Confidence
com.google.cloud:google-cloud-spanner-bom	6.56.0 -> 6.57.0

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Release Notes

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

v6.57.0

Compare Source

Features

• Add FLOAT32 enum to TypeCode (#​2800) (383fea5)
• Add support for Proto Columns (#​2779) (30d37dd)
• spanner: Add proto descriptors for proto and enum types in create/update/get database ddl requests (#​2774) (4a906bf)

Bug Fixes

• Remove google-cloud-spanner-executor from the BOM (#​2844) (655000a)

Dependencies

• Update dependency com.google.cloud:google-cloud-shared-dependencies to v3.22.0 (#​2785) (f689f74)
• Update dependency com.google.cloud:google-cloud-shared-dependencies to v3.23.0 (#​2801) (95f064f)

Documentation

• Samples and tests for instance APIs. (#​2768) (88e24c7)

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