fix: support platform-specific test runtime environment variables (#2941)

Honor platform-specific test runtime settings

Let the shared option reader apply Android and iOS environment overrides, matching the documented configuration precedence.

Constraint: Preserve existing global, TOML, and override behavior for test-runtime.
Rejected: Add Android/iOS-specific lookup code | OptionsReader already implements platform environment precedence.
Confidence: high
Scope-risk: narrow
Directive: Keep test-runtime on the shared option cascade when adding future platforms.
Tested: Focused red/green regression; 824 unit tests; prek all hooks; pylint 10.00/10; diff check.
Not-tested: Android and iOS device integration runs.

Co-authored-by: ychampion <ychampion@users.noreply.github.com>

cibuildwheel/options.py

@@ -821,7 +821,6 @@ class Options:
 
             test_runtime_str = self.reader.get(
                 "test-runtime",
-                env_plat=False,
                 option_format=ShlexTableFormat(sep="; ", pair_sep=":", allow_merge=False),
             )
             if not test_runtime_str:

unit_test/options_test.py

@@ -832,6 +832,31 @@ def test_test_runtime_handling(
     assert local.test_runtime.args == expected_args
 
 
+@pytest.mark.parametrize(
+    ("platform", "platform_envvar"),
+    [
+        ("android", "CIBW_TEST_RUNTIME_ANDROID"),
+        ("ios", "CIBW_TEST_RUNTIME_IOS"),
+    ],
+)
+def test_test_runtime_platform_environment(
+    tmp_path: Path, platform: PlatformName, platform_envvar: str
+) -> None:
+    args = CommandLineArguments.defaults()
+    args.package_dir = tmp_path
+
+    options = Options(
+        platform=platform,
+        command_line_arguments=args,
+        env={
+            "CIBW_TEST_RUNTIME": "args: --global",
+            platform_envvar: "args: --platform-specific",
+        },
+    )
+
+    assert options.build_options(None).test_runtime.args == ["--platform-specific"]
+
+
 @pytest.mark.parametrize(
     ("definition", "expected"),
     [