ci: fix testcase discovery path in test-uipath workflow

[radu-mocanu]

Summary

• point testcase discovery and per-testcase working directory at `uipath-python/packages/uipath/testcases/` instead of the non-existent repo-root `testcases/`

Why

the integration test job was failing before running anything because `find testcases` at the `uipath-python` repo root returned nothing, the matrix fanned out an empty-string testcase entry, and the container tried to chdir into a path that does not exist. the testcases live under `packages/uipath/testcases/` after the mono-repo refactor

[Copilot]

Pull request overview

This PR fixes the GitHub Actions integration-test discovery and execution paths in the test-uipath workflow to point at the actual UiPath Python testcase location under uipath-python/packages/uipath/testcases/, preventing failures due to missing directories.

Changes:

• Update testcase discovery step to run from uipath-python/packages/uipath so find testcases resolves correctly.
• Update per-testcase execution working directory to uipath-python/packages/uipath/testcases/${{ matrix.testcase }}.

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