fix: update module github.com/googleapis/go-sql-spanner to v1.18.0

[renovate-bot]

This PR contains the following updates:

Package	Change	Age	Confidence
github.com/googleapis/go-sql-spanner	v1.17.0 -> v1.18.0

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Release Notes

googleapis/go-sql-spanner (github.com/googleapis/go-sql-spanner)

v1.18.0

Compare Source

Features

• Allow DDL statements with QueryContext (#​515) (aa00055)
• Support BEGIN, COMMIT and ROLLBACK statements (#​520) (e88c303)
• Support read_lock_mode for r/w transactions (#​505) (a552d5e)
• Use a single multiplexed session for all operations (#​500) (8463a6c)

Bug Fixes

• Update all dependencies (#​492) (6dba3cf)
• Update all dependencies (#​510) (31d67ce)
• Update all dependencies (#​519) (3aae705)

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