This breaks tests. More lines need to be changed apparently.

The errors all conform to the following pattern:

3) Symfony\Component\Inflector\Tests\InflectorTest::testPluralize with data set #73 ('matrix', array('matrices', 'matrixes'))
Failed asserting that two arrays are equal.
--- Expected
+++ Actual
@@ @@
 Array (
-    0 => 'matrices'
+    0 => 'matricies'
     1 => 'matrixes'
 )

However, the word matricies does not occur anywhere in the branch where I corrected the spelling. So, from where is the test getting it?

You might want to take inspiration from eg #43790 which fixes something similar for another word.

Unfortunately that does not help. I still do not see from where the test is getting the "matricies" that it's listing in the "Actual" line.

The more overarching question is, why are the tests also failing on other words (fungus, hero) that have nothing to do with the one word I changed in src/Symfony/Component/Inflector/Tests/InflectorTest.php.

Shouldn't those other words cause failures in all CI tests that do not include my word change?