CsvEncoderTest::testDecodeCsv() fails in Drupal 9

Problem/Motivation

The unit tests for this module fail on Drupal 9, potentially due to PHPUnit version.

Steps to reproduce

Run the unit tests on Drupal 9.

Proposed resolution

TBD

Remaining tasks

• Determine what's causing the difference in array keys in the assertion
• Write a patch
• Run weekly tests against PHP 8

User interface changes

N/A

API changes

N/A

Data model changes

N/A