Input key checks are unnecessarily case-sensitive

**Describe the bug**
There are a lot of contexts whose possible input keys are case insensitive. For example, both `secrets.BANANA` and `secrets.banana` work just fine (from the [github secrets docs](https://docs.github.com/en/actions/security-guides/encrypted-secrets#naming-your-secrets): "Names are not case-sensitive."). This applies to secrets, with blocks, and many more. The extension currently erroneously reports an error when not using the same casing as the definition

**To Reproduce**
Steps to reproduce the behavior:
1. Create repo secret called "BANANA"
2. Use secret via secrets.banana

**Expected behavior**
No error is reported

**Screenshots**

**Extension Version**
`v0.25.4`

**Additional context**
-