apollo-compiler: SelectionSet::is_introspection is incorrect when fragments are repeated

[glasser]

Description

The function SelectionSet::is_introspection incorrectly returns false when fragment spreads are repeated at the top level of an operation. For example, this operation should return true from is_introspection, but it does not:

query IntrospectRepeatedIndirectFragment {
  ...A
  ...B
}
fragment A on Root { ...C }
fragment B on Root { ...C }
fragment C on Root {
  __schema {
    types {
      name
    }
  }
}

Steps to reproduce

Will post a PR with a fix and unit tests shortly.

Expected result

The operation above should be considered as introspection and is_introspection should return true.

Actual result

It returns false.

Environment

• Operating system and version: macOS
• Shell (bash/zsh/powershell): bash
• apollo-rs crate: main