go.mod: TestProcessor fails after cloud.google.com/go/spanner update to 1.86

[tarasmadan]

Describe the bug
Updating dependencies in #6414 I faces the problems with TestProcessor.
Spanner dependency downgrade to 1.82 from 1.86 helped.

To Reproduce
go get cloud.google.com/go/spanner
run tests
Or see logs.

[a-nogikh]

I wonder if it's due to some incompatibility between the new version of the cloud.google.com/go/spanner library and the Spanner emulator version from the Docker container:

syzkaller/tools/docker/env/Dockerfile

Lines 93 to 98 in b6605ba

	# Install the Spanner emulator.
	ARG SPANNER_EMULATOR_VERSION=1.5.28
	RUN mkdir /spanner
	RUN curl https://storage.googleapis.com/cloud-spanner-emulator/releases/${SPANNER_EMULATOR_VERSION}/cloud-spanner-emulator_linux_amd64-${SPANNER_EMULATOR_VERSION}.tar.gz | tar -C /spanner -xz
	RUN chmod u+x /spanner/gateway_main /spanner/emulator_main
	ENV SPANNER_EMULATOR_BIN=/spanner/gateway_main

[tarasmadan]

One more place for dependabot to take care about.