`RuntimeWarning: coroutine 'ExecutionContext.execute_fields.<locals>.resolve' was never awaited` on 3.3.0a11

# Description
When executing a query with multiple fields, if an async field's resolver is processed first (its inner `resolve()` coroutine gets stashed for later), and a later sibling `NonNull` field raises synchronously, the exception escapes `execute_fields` immediately, before the stashed coroutine is ever awaited or closed. **This results in:**
```
RuntimeWarning: coroutine 'ExecutionContext.execute_fields..resolve' was never awaited
```

## Environment
- graphql-core: 3.3.0a11
- strawberry-graphql: 0.291.3 (via experimental_execute_incrementally)
- Python: 3.12.13

## Minimal reproduction
```python

from __future__ import annotations

import asyncio
import sys

from graphql import (
GraphQLField,
GraphQLNonNull,
GraphQLObjectType,
GraphQLSchema,
GraphQLString,
parse,
)
from graphql.execution import experimental_execute_incrementally

async def resolve_slow_async(_obj, _info):
await asyncio.sleep(0.01)
return "ok"

def resolve_sync_raises_nonnull(_obj, _info):
raise Exception("boom from sibling")

schema = GraphQLSchema(
query=GraphQLObjectType(
name="Query",
fields={
"slow": GraphQLField(GraphQLString, resolve=resolve_slow_async),
"fast_fail": GraphQLField(
GraphQLNonNull(GraphQLString),
resolve=resolve_sync_raises_nonnull,
),
},
)
)

async def run():
try:
result = experimental_execute_incrementally(
schema=schema,
document=parse("{ slow fast_fail }"),
)
if asyncio.iscoroutine(result):
result = await result
print(f"result: {result!r}")
except Exception as exc:
print(f"raised: {type(exc).__name__}: {exc}")

if __name__ == "__main__":
sys.exit(asyncio.run(run()))

```
## Observed output
```
result: ExecutionResult(data=None, errors=[GraphQLError('boom from sibling', ...)])
sys:1: RuntimeWarning: coroutine 'resolve_slow_async' was never awaited
sys:1: RuntimeWarning: coroutine 'ExecutionContext.complete_awaitable_value' was never awaited
sys:1: RuntimeWarning: coroutine 'ExecutionContext.execute_fields..resolve' was never awaited
```

Start at ExecutionContext.execute_fields and the experimental_execute_incrementally entry point, using the minimal reproduction with the { slow fast_fail } query. Trace how the stashed async resolver and complete_awaitable_value are handled when the sibling NonNull resolver raises. Done means the query still returns the reported execution error without RuntimeWarning messages for unawaited coroutines.

由索引模型根據 Issue 內容生成。