Fix complex (non-scalar) input collections in Java

[leonardehrenfried]

Description

Fix the code generation for complex (non-scalar) input types. Without this you will see ClassCastExceptions when using these types.

Related #1094

Type of change

Please delete options that are not relevant.

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as
  expected)
• This change requires a documentation update

Screenshots/Sandbox (if appropriate/relevant):

Adding links to sandbox or providing screenshots can help us understand more about this PR and take
action on it as appropriate

How Has This Been Tested?

I'm using it in our own project OpenTripPlanner and it works.

CI also passes on my own fork: https://github.com/leonardehrenfried/graphql-code-generator-community/actions/runs/14938404442

Test Environment:

• OS: Linux
• @graphql-codegen/java: 4.0.1
• NodeJS: 22

Checklist:

• I have followed the
  CONTRIBUTING doc and the
  style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• Any dependent changes have been merged and published in downstream modules

Further comments

If this is a relatively large or complex change, kick off the discussion by explaining why you chose
the solution you did and what alternatives you considered, etc...

[changeset-bot]

🦋 Changeset detected

Latest commit: 1a2a57c

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 1 package

Name	Type
@graphql-codegen/java	Patch

Not sure what this means? Click here to learn what changesets are.

Click here if you're a maintainer who wants to add another changeset to this PR