I'm getting the following error which I believe to be mistaken:

object, array, and null values should not be evaluated in template with ${{ }} but evaluating the value of type array<any> [expression]

Here's a minimal reproducer.

The value of matrix.PR is, of course, an array. actionlint doesn't seem to recognise here that I will have a different job dispatched for each entry in the matrix.PR array, and each job will only see one value for matrix.PR.