[py] Fix test for CONDA_PREFIX in selenium_manager

Accessing CONDA_PREFIX in os.environ fails with a KeyError when it is
not set. The condition should instead check for the existence of the
key, before accessing it in the following codepath

Fixes: d4285d1 ("fix for conda install of selenium-manager (SeleniumHQ#12536)")

py/selenium/webdriver/common/selenium_manager.py

@@ -57,7 +57,7 @@ def get_binary() -> Path:
 
             path = Path(__file__).parent.joinpath(directory, file)
 
-        if not path.is_file() and os.environ["CONDA_PREFIX"]:
+        if not path.is_file() and "CONDA_PREFIX" in os.environ:
             # conda has a separate package selenium-manager, installs in bin
             path = Path(os.path.join(os.environ["CONDA_PREFIX"], "bin", file))
             logger.debug("Conda environment detected, using `%s`", path)