renovate: Unwanted go.mod updates to toolchain go1.23.x

[quartzmo]

In the most recent Renovate PR, the following go.mod files were updated to toolchain go1.23.4.

• auth/go.mod
• spanner/test/opentelemetry/test/go.mod
• storage/go.mod
• storage/internal/benchmarks/go.mod

Note that all of these files already had toolchain go1.22.x directives present, of unknown origin.

Due to this update, the post-processor job in #11456 failed with the following message:

Step #5: 2025/01/17 01:16:57 go: go: module cache not found: neither GOMODCACHE nor GOPATH is set
Step #5: 
Step #5: 2025/01/17 01:16:57 unable to build docs URL: exit status 1

Removing (not restoring) the toolchain go1.23.x directives in all go.mod files fixed the broken job.

This issue may be closed if it is determined that Renovate does not add toolchain go1.23.x directives, but only updates them if already present.

No go.mod file should be checked in with a newly added toolchain directive. Please check your changes to go.mod files to prevent this from happening.