Unexpected query translation with in-between projection and nullable foreign keys

### Question

Hello,

This probably isn't a bug, but found a slightly unexpected query translation in the example code.

The produced query is:
```sql
SELECT t."Id" AS "ThingId", i."Amount" AS "ItemAmount", (
SELECT COALESCE(sum(i0."Amount"), 0.0)
FROM "Item2s" AS i0
WHERE i0."ItemId" = i."Id" OR (i0."ItemId" IS NULL AND i."Id" IS NULL)) AS "Item2Amount"
FROM "Things" AS t
LEFT JOIN "Items" AS i ON t."Id" = i."ThingId"
```

The unexpected part is the additional null check ` OR (i0."ItemId" IS NULL AND i."Id" IS NULL)` which includes unintended rows in the final value of `Item2Amount`.

The query I thought would be produced is the one produced by changing the left join into a regular (inner) join:
```sql
SELECT t."Id" AS "ThingId", i."Amount" AS "ItemAmount", (
SELECT COALESCE(sum(i0."Amount"), 0.0)
FROM "Item2s" AS i0
WHERE i0."ItemId" = i."Id") AS "Item2Amount"
FROM "Things" AS t
INNER JOIN "Items" AS i ON t."Id" = i."ThingId"
```

I don't think there should be a difference whether using left or inner join, at least when the sum is calculated using a non-nullable property (maybe if I would join against a NULL column then one would expect the null addition), but maybe my intuition is wrong and this is the intended behaviour.

What I actually thought EF would produce is more like this:
```sql
SELECT t."Id" AS "ThingId", i."Amount" AS "ItemAmount", i."Item2Amount"
FROM "Things" AS t
LEFT JOIN (
SELECT i."Id", i."ThingId", i."Amount", (SELECT sum(i0."Amount") FROM "Item2s" as I0 WHERE i0."ItemId" = i."Id") as "Item2Amount"
FROM "Items" AS i
) AS i ON t."Id" = i."ThingId"
```

Thank you for any clarification. If this behaviour is intended, then I will just have to remember to add a null check even if in sql that check is unnecessary. At least I don't think there is any way to not have the additional OR condition (tried with `y.ItemId!.Value == x.Id` or even casting to int, but didn't remove the OR)?

I don't think this is related to Postgresql provider so created "issue" here.

### Your code

```csharp
using var db = new AppDbContext(contextOptions.Options);
db.Database.EnsureCreated();

var result = db.Things
.LeftJoin(
db.Items
.Select(x => new
{
Item = x,
Item2Total = (decimal?)db.Item2s
.Where(y => y.ItemId == x.Id)
.Sum(y => y.Amount),
}),
x => x.Id,
y => y.Item.ThingId,
(x, y) => new
{
ThingId = x.Id,
ItemAmount = (decimal?)y!.Item.Amount,
Item2Amount = y.Item2Total,
})
.ToList();

public class AppDbContext : DbContext
{
public AppDbContext(DbContextOptions options) : base(options) { }

public DbSet Things { get; set; }
public DbSet Items { get; set; }
public DbSet Item2s { get; set; }

protected override void OnModelCreating(ModelBuilder modelBuilder)
{
modelBuilder.Entity()
.HasKey(x => x.Id);

modelBuilder.Entity()
.HasMany()
.WithOne()
.HasForeignKey(x => x.ThingId);

modelBuilder.Entity()
.HasKey(x => x.Id);

modelBuilder.Entity()
.HasMany()
.WithOne()
.HasForeignKey(x => x.ItemId);

modelBuilder.Entity()
.HasKey(x => x.Id);

}
}

public class Thing
{
public int Id { get; set; }
}

public class Item
{
public int Id { get; set; }
public int ThingId { get; set; }
public decimal Amount { get; set; }
}

public class Item2
{
public int Id { get; set; }
public int? ItemId { get; set; }
public decimal Amount { get; set; }
}
```

### Stack traces

```text

```

### Verbose output

```text

```

### EF Core version

10

### Database provider

Npgsql.EntityFrameworkCore.PostgreSQL

### Target framework

10

### Operating system

_No response_

### IDE

_No response_