opentelemetry-proto local own dependency not found

[eguzki]

Describe your environment

• Ubuntu 20.04 cmake version 3.16.3
• RHEL 8.5 cmake version 3.20.2-4.el8
• Ubuntu 20.04 cmake version 3.25.0 (latest as of today)

Tested with opentelemetry-cpp latest (as of today) and opentelemetry-proto v0.19.0

Steps to reproduce
Building with OTELCPP_PROTO_PATH set

cmake -DOTELCPP_PROTO_PATH=/path/to/proto ..

What is the expected behavior?
local opentelemetry dependency is found and used to build opentelemetry-cpp

What is the actual behavior?
it always fails with "not existing" error

CMake Error at cmake/opentelemetry-proto.cmake:30 (message):
  OTELCPP_PROTO_PATH does not point to a opentelemetry-proto repository
Call Stack (most recent call first):
  CMakeLists.txt:328 (include)

Additional context
Add any other context about the problem here.