Ignore whitespace for annotation diffs

[nwiltsie]

The expected and actual results are compared in two ways:

1. The workflow's pass/fail status is driven by comparing the parsed/in-memory values
2. The annotations are driven by the output of diff expected.json actual.json

The workflow itself writes out files with a very standardized JSON format, but user modifications to the file(s) can lead to weirdness like https://github.com/uclahs-cds/pipeline-calculate-targeted-coverage/actions/runs/8239656461/job/22533387375?pr=56, where the tests pass but there are a ton of annotations complaining of differences.

Using diff -w to ignore whitespace for those annotations should fix the problem.