tests: Force analysis test labels to resolve within @rules_python context (#1187)

When a string label is passed to the `@rules_testing` analysis_test
functions, the strings are evaluated within the context of
@rules_testing because that is where the actual rule invocation happens.
Without bzlmod, this just requires qualifying the labels with the repo
name (which is what was being done) because there's just a flat global
namespace of repos.

With bzlmod enabled, repo mapping happens, so rules_testing tries to
resolve those repo names using its repo mapping, which doesn't work
because rules_testing's mapping doesn't include every repo using it.

tools/build_defs/python/tests/py_test/py_test_tests.bzl

diff --git a/tools/build_defs/python/tests/py_test/py_test_tests.bzl b/tools/build_defs/python/tests/py_test/py_test_tests.bzl
index 5608832..8bb2fc2 100644
--- a/tools/build_defs/python/tests/py_test/py_test_tests.bzl
+++ b/tools/build_defs/python/tests/py_test/py_test_tests.bzl
@@ -22,6 +22,12 @@
 )
 load("//tools/build_defs/python/tests:util.bzl", pt_util = "util")
 
+# Explicit Label() calls are required so that it resolves in @rules_python context instead of
+# @rules_testing context.
+_FAKE_CC_TOOLCHAIN = Label("//tools/build_defs/python/tests:cc_toolchain_suite")
+_PLATFORM_MAC = Label("//tools/build_defs/python/tests:mac")
+_PLATFORM_LINUX = Label("//tools/build_defs/python/tests:linux")
+
 _tests = []
 
 def _test_mac_requires_darwin_for_execution(name, config):
@@ -44,8 +50,8 @@
         target = name + "_subject",
         config_settings = {
             "//command_line_option:cpu": "darwin_x86_64",
-            "//command_line_option:crosstool_top": "@rules_python//tools/build_defs/python/tests:cc_toolchain_suite",
-            "//command_line_option:platforms": "@rules_python//tools/build_defs/python/tests:mac",
+            "//command_line_option:crosstool_top": _FAKE_CC_TOOLCHAIN,
+            "//command_line_option:platforms": [_PLATFORM_MAC],
         },
     )
 
@@ -75,8 +81,8 @@
         target = name + "_subject",
         config_settings = {
             "//command_line_option:cpu": "k8",
-            "//command_line_option:crosstool_top": "@rules_python//tools/build_defs/python/tests:cc_toolchain_suite",
-            "//command_line_option:platforms": "@rules_python//tools/build_defs/python/tests:linux",
+            "//command_line_option:crosstool_top": _FAKE_CC_TOOLCHAIN,
+            "//command_line_option:platforms": [_PLATFORM_LINUX],
         },
     )