opentelemetry-test-utils: skip installing grpc exporter only on Pypy (open-telemetry#5178)

* opentelemetry-test-utils: move requirements environment markers to a constraint file

For some reason dependabot fails parsing them.

* Second try

* Apply suggestions from code review

Co-authored-by: Emídio Neto <9735060+emdneto@users.noreply.github.com>

* Update tox.ini

* Update dependency paths in test-requirements.txt

Change paths for dependencies in test-requirements.txt

* Skip only on pypy since installation of requirements on windows seems to work

---------

Co-authored-by: Emídio Neto <9735060+emdneto@users.noreply.github.com>

Author: xrmx

tests/opentelemetry-test-utils/test-requirements.txt

@@ -14,8 +14,7 @@ zipp==3.19.2
 -e opentelemetry-semantic-conventions
 -e tests/opentelemetry-test-utils
 # these are required for weaver integration tests, we're running that only on linux / CPython
-# because of lack of support for gRPC on Windows in some cases.
-# note: tox does not support PEP 508 markers on `-e` editable installs, so these are installed non-editable
-./opentelemetry-proto ; sys_platform != 'win32' and platform_python_implementation != 'PyPy'
-./exporter/opentelemetry-exporter-otlp-proto-common ; sys_platform != 'win32' and platform_python_implementation != 'PyPy'
-./exporter/opentelemetry-exporter-otlp-proto-grpc ; sys_platform != 'win32' and platform_python_implementation != 'PyPy'
+# because of lack of support for gRPC wheels on some platforms
+./opentelemetry-proto ; platform_python_implementation != 'PyPy'
+./exporter/opentelemetry-exporter-otlp-proto-common ; platform_python_implementation != 'PyPy'
+./exporter/opentelemetry-exporter-otlp-proto-grpc ; platform_python_implementation != 'PyPy'