trac #33531: don't run pytest by default

Since running pytest is broken right now (see #31924, #32975, ...), we
don't run pytest by default anymore.

In order to run pytest one has to use the feature flag "pytest", for
instance:

    $ ./sage -t --optional=pytest src/sage/numerical/backends/cvxopt_backend_test.py

This will run only pytest; one can use --optional=sage,pytest to run both.

src/bin/sage-runtests

@@ -145,21 +145,22 @@ if __name__ == "__main__":
     DC = DocTestController(args, args.filenames)
     err = DC.run()
 
-    try:
-        exit_code_pytest = 0
-        import pytest
-        pytest_options = ["--import-mode", "importlib"]
-        if args.verbose:
-            pytest_options.append("-v")
-        exit_code_pytest = pytest.main(pytest_options + args.filenames)
-        if exit_code_pytest == 5:
-            # Exit code 5 means there were no test files, pass in this case
+    if "pytest" in DC.options.optional:
+        try:
             exit_code_pytest = 0
-
-    except ModuleNotFoundError:
-        print("Pytest is not installed, skip checking tests that rely on it.")
-
-    if err == 0:
-        sys.exit(exit_code_pytest)
-    else:
-        sys.exit(err)
+            import pytest
+            pytest_options = ["--import-mode", "importlib"]
+            if args.verbose:
+                pytest_options.append("-v")
+            exit_code_pytest = pytest.main(pytest_options + args.filenames)
+            if exit_code_pytest == 5:
+                # Exit code 5 means there were no test files, pass in this case
+                exit_code_pytest = 0
+
+        except ModuleNotFoundError:
+            print("Pytest is not installed, skip checking tests that rely on it.")
+
+        if err == 0:
+            sys.exit(exit_code_pytest)
+
+    sys.exit(err)