`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.

Written by the indexing model from the issue text.