chore(deps): update dependency google-cloud-spanner to v3.12.0

[renovate-bot]

This PR contains the following updates:

Package	Change	Age	Adoption	Passing	Confidence
google-cloud-spanner	== 3.11.1 -> ==3.12.0

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Release Notes

googleapis/python-spanner

v3.12.0

Compare Source

Features

• add context manager support in client (5ae4be8)
• add context manager support in client (#​637) (5ae4be8)
• add support for python 3.10 (#​626) (17ca61b), closes #​623
• db_api: add an ability to set ReadOnly/ReadWrite connection mode (#​475) (cd3b950)
• db_api: make rowcount property NotImplemented (#​603) (b5a567f)
• db_api: raise exception with message for executemany() (#​595) (95908f6)
• db_api: support JSON data type (#​627) (d760c2c)
• db_api: support stale reads (#​584) (8ca868c)

Bug Fixes

• db_api: emit warning instead of an exception for rowcount property (#​628) (62ff9ae)
• deps: drop packaging dependency (5ae4be8)
• deps: require google-api-core >= 1.28.0 (5ae4be8)
• improper types in pagers generation (5ae4be8)

Performance Improvements

• dbapi: set headers correctly for dynamic routing (#​644) (d769ff8)

Documentation

• list oneofs in docstring (5ae4be8)

3.11.1 (2021-10-04)

Bug Fixes

• add support for json data type (#​593) (bc5ddc3)
• remove database_version_time param from test_instance_list_backups (#​609) (db63aee)

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[vi3k6i5]

Closing this as 12.0 had a breaking change. More details here #746