[Impeller] Disable impeller_unittests. (flutter#38307)

Fixes flutter/flutter#114872
Followup in flutter/flutter#117122

testing/run_tests.py

@@ -440,26 +440,28 @@ def make_test(name, flags=None, extra_env=None):
         shuffle_flags,
         coverage=coverage
     )
+    # TODO(117122): Re-enable impeller_unittests after shader compiler errors
+    #               are addressed.
     # Impeller tests are only supported on macOS for now.
-    run_engine_executable(
-        build_dir,
-        'impeller_unittests',
-        executable_filter,
-        shuffle_flags,
-        coverage=coverage,
-        extra_env={
-            # pylint: disable=line-too-long
-            # See https://developer.apple.com/documentation/metal/diagnosing_metal_programming_issues_early?language=objc
-            'MTL_SHADER_VALIDATION':
-                '1',  # Enables all shader validation tests.
-            'MTL_SHADER_VALIDATION_GLOBAL_MEMORY':
-                '1',  # Validates accesses to device and constant memory.
-            'MTL_SHADER_VALIDATION_THREADGROUP_MEMORY':
-                '1',  # Validates accesses to threadgroup memory.
-            'MTL_SHADER_VALIDATION_TEXTURE_USAGE':
-                '1',  # Validates that texture references are not nil.
-        }
-    )
+    # run_engine_executable(
+    #     build_dir,
+    #     'impeller_unittests',
+    #     executable_filter,
+    #     shuffle_flags,
+    #     coverage=coverage,
+    #     extra_env={
+    #         # pylint: disable=line-too-long
+    #         # See https://developer.apple.com/documentation/metal/diagnosing_metal_programming_issues_early?language=objc
+    #         'MTL_SHADER_VALIDATION':
+    #             '1',  # Enables all shader validation tests.
+    #         'MTL_SHADER_VALIDATION_GLOBAL_MEMORY':
+    #             '1',  # Validates accesses to device and constant memory.
+    #         'MTL_SHADER_VALIDATION_THREADGROUP_MEMORY':
+    #             '1',  # Validates accesses to threadgroup memory.
+    #         'MTL_SHADER_VALIDATION_TEXTURE_USAGE':
+    #             '1',  # Validates that texture references are not nil.
+    #     }
+    # )
 
 
 def parse_impeller_vulkan_filter():