Errors in the Capitalization of keys is not detected as an error

[pmav99]

actionlint does not seem to detect errors in the capitalization of keys. For example run vs ruN. The latter prevents the action from running altogether with the following error:

Error: .github#L1
every step must define a `uses` or `run` key

Nevertheless, actionlint says that there are no issues whatsoever.

Sample yaml file:

---

name: "Action Name"

on:
  push:

jobs:
  run_tests:
    name: "Test stacked environments"
    runs-on: "ubuntu-latest"

    steps:
      - ruN: echo "${PATH}"

[rhysd]

Some keys are case sensitive and some other keys are not. This needs more investigation.