fix ruff: move yaml import to top level

Assisted-by: Claude Sonnet 4.6

Author: MikeGoldsmith

opentelemetry-sdk/tests/_configuration/file/test_env_substitution.py

@@ -16,6 +16,8 @@
 import unittest
 from unittest.mock import patch
 
+import yaml
+
 from opentelemetry.sdk._configuration.file import (
     EnvSubstitutionError,
     substitute_env_vars,
@@ -123,8 +125,6 @@ def test_newline_in_value_prevents_yaml_injection(self):
         environment variables." A value like "legit\\nmalicious_key: val"
         must be emitted as a quoted scalar, not raw YAML.
         """
-        import yaml
-
         with patch.dict(
             os.environ,
             {"SERVICE_NAME": "legit-service\nmalicious_key: injected_value"},
@@ -138,34 +138,24 @@ def test_newline_in_value_prevents_yaml_injection(self):
 
     def test_newline_in_value_preserved_as_literal(self):
         """Newline within a value is preserved as a literal newline character."""
-        import yaml
-
         with patch.dict(os.environ, {"MULTI": "line1\nline2"}):
             result = substitute_env_vars("key: ${MULTI}")
         parsed = yaml.safe_load(result)
         self.assertEqual(parsed["key"], "line1\nline2")
 
     def test_carriage_return_in_value_is_escaped(self):
         """Carriage return in value is escaped, not injected."""
-        import yaml
-
         with patch.dict(os.environ, {"VAL": "text\r\nmore"}):
             result = substitute_env_vars("key: ${VAL}")
         parsed = yaml.safe_load(result)
         self.assertIsInstance(parsed["key"], str)
 
     def test_type_coercion_preserved_for_simple_values(self):
         """Simple values without newlines still undergo YAML type coercion per spec."""
-        import yaml
-
-        with patch.dict(
-            os.environ, {"BOOL_VAL": "true", "INT_VAL": "42"}
-        ):
+        with patch.dict(os.environ, {"BOOL_VAL": "true", "INT_VAL": "42"}):
             bool_result = yaml.safe_load(
                 substitute_env_vars("key: ${BOOL_VAL}")
             )
-            int_result = yaml.safe_load(
-                substitute_env_vars("key: ${INT_VAL}")
-            )
+            int_result = yaml.safe_load(substitute_env_vars("key: ${INT_VAL}"))
         self.assertIs(bool_result["key"], True)
         self.assertEqual(int_result["key"], 42)