chore: Make sure demo apps run using gRPC OTLP endpoint

It created a deadlock with the gRPC instrumentation and I cut some corners. I'm planning to send a subsequent PR for this. I will create an issue.

_Originally posted by @kakkoyun in https://github.com/open-telemetry/opentelemetry-go-compile-instrumentation/pull/226#discussion_r2606903860_
            