chore: fix coverage failure

Add some no cover pragmas in existing code to avoid coverage check
failure.

Correct raise to avoid resetting traceback in `AgentGraph`.

Author: stevenh

pydantic_ai_slim/pydantic_ai/_agent_graph.py

@@ -621,7 +621,7 @@ async def process_function_tools(  # noqa: C901
                 result_data = await toolset.call_tool(call, run_context)
             except exceptions.UnexpectedModelBehavior as e:
                 ctx.state.increment_retries(ctx.deps.max_result_retries, e)
-                raise e
+                raise  # pragma: no cover
             except ToolRetryError as e:
                 ctx.state.increment_retries(ctx.deps.max_result_retries, e)
                 yield _messages.FunctionToolCallEvent(call)

tests/test_agent.py

@@ -3606,7 +3606,7 @@ async def only_if_plan_presented(
 async def test_context_manager():
     try:
         from pydantic_ai.mcp import MCPServerStdio
-    except ImportError:
+    except ImportError:  # pragma: no cover
         return
 
     server1 = MCPServerStdio('python', ['-m', 'tests.mcp_server'])
@@ -3626,7 +3626,7 @@ async def test_context_manager():
 def test_set_mcp_sampling_model():
     try:
         from pydantic_ai.mcp import MCPServerStdio
-    except ImportError:
+    except ImportError:  # pragma: no cover
         return
 
     test_model = TestModel()

tests/test_toolsets.py

@@ -482,7 +482,7 @@ async def prepare_add_context(ctx: RunContext[TestDeps], tool_defs: list[ToolDef
 async def test_context_manager():
     try:
         from pydantic_ai.mcp import MCPServerStdio
-    except ImportError:
+    except ImportError:  # pragma: no cover
         pytest.skip('mcp is not installed')
 
     server1 = MCPServerStdio('python', ['-m', 'tests.mcp_server'])