Fragment name clashes with field name

**Describe the bug**

I am trying to generate the Golang model for a Graphql fragment like so:

```json
fragment loginMethods on Customer {
loginMethods {
... on PassKeyMethod {
...
... on PasswordMethod {
...
}
... on EmailMethod {
...
}
}
}
```

After running `$ go run github.com/Khan/genqlient@main ./genqlient.yaml`, I see that there is a clash in the structs that are generated:

```golang
func (v *LoginMethods) UnmarshalJSON(b []byte) error {
if string(b) == "null" {
return nil
}

var firstPass struct {
*LoginMethods
LoginMethods []json.RawMessage `json:"loginMethods"`. <<<-------- 2 fields in the struct with same name!!
graphql.NoUnmarshalJSON
}
firstPass.LoginMethods = v
```

My `genqlient.yaml` is as follows:

```yaml
# Base template at
# https://github.com/Khan/genqlient/blob/main/docs/genqlient.yaml; refer to the
# template for description of each field.

# Specify where the GrpahQL schema is located.
schema: ./schema.graphql

# Specify the GraphQL operations (queries, mutations, subscriptions) are
# located.
operations:
- ./**/*.graphql

# Specify the filename to which to write the generated code, relative to
# genqlient.yaml. Default: generated.go.
generated: ../../model/android/generated/genqlient.go

# Other config parameters.
use_struct_references: true
optional: pointer_omitempty
bindings:
DateTime:
type: time.Time
Timestamp:
type: time.Time
casing:
# Specify the casing algorithm to use for all GraphQL names (fields, types,
# etc.).
default: auto_camel_case
all_enums: raw
```

**To Reproduce**
Generate the Golang code for specified model; unfortunately I cannot share `schema.graphql`, I can spend some time to handcraft an example schema.graphql if required.

**Expected behavior**
Struct fields should have unique names, as otherwise this fails compilation.

**genqlient version**
Latest from `master`, my `go.mod` has `github.com/Khan/genqlient v0.8.2-0.20251119064104-5b0aabc933fa`

Start with the GraphQL fragment and field names in the issue, then run `go run github.com/Khan/genqlient@main ./genqlient.yaml` using the described `genqlient.yaml` and a minimized `schema.graphql`. Inspect the generated `genqlient.go` at the configured output path and the generated `LoginMethods` struct. Done means the generated Go code gives the fragment and field unique struct names and compiles.

Written by the indexing model from the issue text.