Update grpc to 1.69.2 to fix dependency problem

[quentinmit]

grpc briefly had a separate module for
google.golang.org/grpc/stats/opentelemetry; because the module was now deleted, Go can't properly resolve dependencies with errors such as:

go: github.com/GoogleCloudPlatform/opentelemetry-operations-collector/service imports
        github.com/open-telemetry/opentelemetry-collector-contrib/exporter/googlecloudexporter imports
        github.com/GoogleCloudPlatform/opentelemetry-operations-go/exporter/collector imports
        google.golang.org/grpc/stats/opentelemetry: ambiguous import: found package google.golang.org/grpc/stats/opentelemetry in multiple modules:
        google.golang.org/grpc v1.69.2 (/usr/local/google/home/quentin/go/pkg/mod/google.golang.org/grpc@v1.69.2/stats/opentelemetry)
        google.golang.org/grpc/stats/opentelemetry v0.0.0-20240702152247-2da976983bbb (/usr/local/google/home/quentin/go/pkg/mod/google.golang.org/grpc/stats/opentelemetry@v0.0.0-20240702152247-2da976983bbb)