Update module cloud.google.com/go/spanner to v1.78.0

[renovate]

This PR contains the following updates:

Package	Change	Age	Adoption	Passing	Confidence
cloud.google.com/go/spanner	v1.32.0 -> v1.78.0

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[renovate]

ℹ Artifact update notice

File name: go.mod

In order to perform the update(s) described in the table above, Renovate ran the go get command, which resulted in the following additional change(s):

• 2 additional dependencies were updated
• The go directive was updated for compatibility reasons

Details:

Package	Change
go	1.16 -> 1.24.1
cloud.google.com/go	v0.100.2 -> v0.120.0
github.com/stretchr/testify	v1.7.0 -> v1.10.0