Only run docs CI when docs changed (#5556)

## Description

This makes it so the Docs CI checks only happen when a PR includes
changes to files under `docs/`

## Checklist

- [ ] I have linked to any relevant issues.
- [ ] I have commented my code, particularly in hard-to-understand
areas.
- [ ] I have updated the documentation where relevant (API docs, the
reference, and the Sway book).
- [ ] I have added tests that prove my fix is effective or that my
feature works.
- [ ] I have added (or requested a maintainer to add) the necessary
`Breaking*` or `New Feature` labels where relevant.
- [ ] I have done my best to ensure that my PR adheres to [the Fuel Labs
Code Review
Standards](https://github.com/FuelLabs/rfcs/blob/master/text/code-standards/external-contributors.md).
- [ ] I have requested a review from the relevant team or maintainers.

Author: sdankel

.github/workflows/docs.yml

@@ -1,12 +1,9 @@
 name: Docs
 
 on:
-  push:
-    branches:
-      - master
   pull_request:
-  release:
-    types: [published]
+    paths:
+      - docs/**
 
 jobs:
   test: