tests(runfiles): migrate runfiles tests to pytest_test (#4061)

Migrate the primary runfiles test targets to pytest_test to standardize
test execution and runner behavior across the test suite.

The main runfiles_test and pathlib_test targets are updated to use
pytest_test. However, the corresponding _min_python_test targets remain
standard py_test targets using standard library unittest. In WORKSPACE
mode, dev_pip dependencies only resolve for Python 3.11, so pytest is
unavailable when testing against Python 3.10; retaining py_test ensures
minimum Python version verification continues to work.

tests/runfiles/BUILD.bazel

diff --git a/tests/runfiles/BUILD.bazel b/tests/runfiles/BUILD.bazel
index 505b3c1..04d7f1a 100644
--- a/tests/runfiles/BUILD.bazel
+++ b/tests/runfiles/BUILD.bazel
@@ -1,8 +1,9 @@
 load("@bazel_skylib//rules:build_test.bzl", "build_test")
 load("@rules_python//python:py_test.bzl", "py_test")
 load("@rules_python//python/private:bzlmod_enabled.bzl", "BZLMOD_ENABLED")  # buildifier: disable=bzl-visibility
+load("//tests/support/pytest_test:pytest_test.bzl", "pytest_test")
 
-py_test(
+pytest_test(
     name = "runfiles_test",
     srcs = ["runfiles_test.py"],
     data = [
@@ -28,7 +29,7 @@
     deps = ["//python/runfiles"],
 )
 
-py_test(
+pytest_test(
     name = "pathlib_test",
     srcs = ["pathlib_test.py"],
     deps = ["//python/runfiles"],