Do not break on very long command-line options

`_set_initial_conftests` could break on some systems if a very long
option was passed, because the `Path.exists()` call raises an
`OSError` instead of returning `False`.

Fix #10169

testing/test_collection.py

@@ -1254,7 +1254,7 @@ def test_initial_conftests_with_testpaths(pytester: Pytester) -> None:
         textwrap.dedent(
             """
             def pytest_sessionstart(session):
-                raise Exception("pytest_sessionstart hook is successfully run")
+                raise Exception("pytest_sessionstart hook successfully run")
             """
         )
     )
@@ -1266,10 +1266,29 @@ def test_initial_conftests_with_testpaths(pytester: Pytester) -> None:
     )
     result = pytester.runpytest()
     result.stdout.fnmatch_lines(
-        "INTERNALERROR* Exception: pytest_sessionstart hook is successfully run"
+        "INTERNALERROR* Exception: pytest_sessionstart hook successfully run"
     )
 
 
+def test_large_option_breaks_initial_conftests(pytester: Pytester) -> None:
+    """Long option values do not break initial conftests handling (#10169)."""
+    option_value = "x" * 1024 * 1000
+    pytester.makeconftest(
+        """
+        def pytest_addoption(parser):
+            parser.addoption("--xx", default=None)
+        """
+    )
+    pytester.makepyfile(
+        f"""
+        def test_foo(request):
+            assert request.config.getoption("xx") == {option_value!r}
+        """
+    )
+    result = pytester.runpytest(f"--xx={option_value}")
+    assert result.ret == 0
+
+
 def test_collect_symlink_file_arg(pytester: Pytester) -> None:
     """Collect a direct symlink works even if it does not match python_files (#4325)."""
     real = pytester.makepyfile(