MultiSourceReader has breaking behavioural changes when running on Java 16+

[jord1e]

Describe the bug
Because of JDK-8241020 "LineNumberReader.getLineNumber() behavior is inconsistent with respect to EOF", the MultiSourceReader class behaves incorrectly when running on Java 16+ VMs, even when compiling with Java 8. This causes breaking changes.

The following test cases are failing:

To Reproduce

Run the tests on JDK 16, or higher
Same issue occurs when you compile on JDK 8 and run tests on JDK 16+ (see results below)

For ease of testing you may temporarily clone https://github.com/jord1e/graphql-java/tree/ci-improvements and change the versions in gradle.properties (or checkout jord1e@a1f4f84)

Results can be downloaded here:
https://github.com/jord1e/graphql-java/actions/runs/1778419182

Found whilst working on #2676

Can't figure this one out on myself quickly...

[github-actions]

Hello, this issue has been inactive for 60 days, so we're marking it as stale. If you would like to continue this discussion, please comment within the next 30 days or we'll close the issue.

[jord1e]

.