Convert swagger release fixture to env var (ansible#14940)

`pytest awx/main/tests/docs --release=$(VERSION_TARGET)`
where --release is required breaks test discovery and running in vscode (from within the container)

Makefile

@@ -305,7 +305,7 @@ swagger: reports
 	@if [ "$(VENV_BASE)" ]; then \
 		. $(VENV_BASE)/awx/bin/activate; \
 	fi; \
-	(set -o pipefail && py.test $(PYTEST_ARGS) awx/conf/tests/functional awx/main/tests/functional/api awx/main/tests/docs --release=$(VERSION_TARGET) | tee reports/$@.report)
+	(set -o pipefail && py.test $(PYTEST_ARGS) awx/conf/tests/functional awx/main/tests/functional/api awx/main/tests/docs | tee reports/$@.report)
 
 check: black
 

awx/main/tests/docs/conftest.py

@@ -1,13 +1,8 @@
 from awx.main.tests.functional.conftest import *  # noqa
+import os
+import pytest
 
 
-def pytest_addoption(parser):
-    parser.addoption("--release", action="store", help="a release version number, e.g., 3.3.0")
-
-
-def pytest_generate_tests(metafunc):
-    # This is called for every test. Only get/set command line arguments
-    # if the argument is specified in the list of test "fixturenames".
-    option_value = metafunc.config.option.release
-    if 'release' in metafunc.fixturenames and option_value is not None:
-        metafunc.parametrize("release", [option_value])
+@pytest.fixture()
+def release():
+    return os.environ.get('VERSION_TARGET', '')