Python tests: skip the session hooks if --collect-only is used (#5550)

Turns out that #5456 had a nasty side effect. Session hooks are called
when pytest is run with `--collect-only` (even though no tests are
actually run in this case), and Visual Studio Code periodically runs
`pytest --collect-only` in order to learn what tests exist in the
project. As a result, it keeps restarting the services and restoring the
database in the background.

Work around this by skipping all logic in the hooks if `--collect-only`
is in the options.

tests/python/shared/fixtures/init.py

@@ -259,12 +259,21 @@ def start_services(rebuild=False):
     docker_cp(CVAT_DB_DIR / "data.json", f"{PREFIX}_cvat_server_1:/tmp/data.json")
 
 
-def pytest_sessionstart(session):
+def pytest_sessionstart(session: pytest.Session) -> None:
     stop = session.config.getoption("--stop-services")
     start = session.config.getoption("--start-services")
     rebuild = session.config.getoption("--rebuild")
     cleanup = session.config.getoption("--cleanup")
     dumpdb = session.config.getoption("--dumpdb")
+
+    if session.config.getoption("--collect-only"):
+        if any((stop, start, rebuild, cleanup, dumpdb)):
+            raise Exception(
+                """--collect-only is not compatible with any of the other options:
+                --stop-services --start-services --rebuild --cleanup --dumpdb"""
+            )
+        return  # don't need to start the services to collect tests
+
     platform = session.config.getoption("--platform")
 
     if platform == "kube" and any((stop, start, rebuild, cleanup, dumpdb)):
@@ -338,7 +347,10 @@ def pytest_sessionstart(session):
         )
 
 
-def pytest_sessionfinish(session, exitstatus):
+def pytest_sessionfinish(session: pytest.Session, exitstatus: int) -> None:
+    if session.config.getoption("--collect-only"):
+        return
+
     platform = session.config.getoption("--platform")
 
     if platform == "local":