Use shell=True for linux to fix conde feedstock runner issue

The issue with conda feedstock runners is they use some variable for
abspath, which doesn't get correctly expanded by `os.path.expandvar`.

This requires using `shell=True` for linux as well.

python/tests/compat/conftest.py

@@ -23,8 +23,15 @@ def is_running_on_windows():
 
 def run_shell_command(command : List[Union[str, os.PathLike]], cwd : Optional[os.PathLike] = None) -> subprocess.CompletedProcess:
     logger.info(f"Executing command: {command}")
-    # shell=True is required for running the correct python executable on Windows
-    result = subprocess.run(command, cwd=cwd, capture_output=True, shell=is_running_on_windows())
+    result = None
+    if is_running_on_windows():
+        # shell=True is required for running the correct python executable on Windows
+        result = subprocess.run(command, cwd=cwd, capture_output=True, shell=True)
+    else:
+        # On linux we need shell=True for conda feedstock runners (because otherwise they fail to expand path variables)
+        # But to correctly work with shell=True we need a single command string.
+        command_string = ' '.join(command)
+        result = subprocess.run(command_string, cwd=cwd, capture_output=True, shell=True, stdin=subprocess.DEVNULL)
     if result.returncode != 0:
         logger.warning(f"Command failed, stdout: {str(result.stdout)}, stderr: {str(result.stderr)}")
     return result
@@ -146,10 +153,7 @@ def assert_read(self, sym : str, df) -> None:
 def old_venv(request):
     version = request.param
     path = os.path.join("venvs", version)
-    # We need to expandvars because on some systems (e.g. Conda Feedstock) abspath uses env variables.
-    requirements_file = os.path.expandvars(
-        os.path.abspath(os.path.join("tests", "compat", f"requirements-{version}.txt"))
-    )
+    requirements_file = os.path.abspath(os.path.join("tests", "compat", f"requirements-{version}.txt"))
     with Venv(path, requirements_file, version) as old_venv:
         yield old_venv