Refactor use of changedir in tox.ini

[ocelotl]

This is necessary to solve an issue with #3742:

In order to run lint we need responses, which is present here. responses was previously in the pyproject.toml file but only as a test dependency.

So, I am fixing this by running lint with pinned dependencies by using a requirements file (which we should do anyways). The problem is that these files right now have lines like these at the end:

-e ../../../opentelemetry-proto
-e ../../../exporter/opentelemetry-exporter-otlp-proto-common
-e ../../../exporter/opentelemetry-exporter-otlp-proto-http

The change of directories at the beginning of every one of those lines is necessary because we have changedir in the tox.ini file. But when lint is executed, there is no corresponding changedir section for lint so, installation fails because the dependency paths cannot be resolved.

To solve this issue, it is necessary to remove the changedir section from tox.ini and instead use a separate pytest command with the complete path of the test folder for every component.