Update documentation to fix github cache key (#29983)

`?` is any optional character, it isn't the same as the `?` in regex which will match the preceding character 0 or more times.



## Bug

- [ ] Related issues linked using `fixes #number`
- [ ] Integration tests added
- [ ] Errors have helpful link attached, see `contributing.md`

## Feature

- [ ] Implements an existing feature request or RFC. Make sure the feature request has been accepted for implementation before opening a PR.
- [ ] Related issues linked using `fixes #number`
- [ ] Integration tests added
- [ ] Documentation added
- [ ] Telemetry added. In case of a feature if it's used or not.
- [ ] Errors have helpful link attached, see `contributing.md`

## Documentation / Examples

- [x] Make sure the linting passes

errors/no-cache.md

@@ -82,7 +82,7 @@ uses: actions/cache@v2
 with:
   path: ${{ github.workspace }}/.next/cache
   # Generate a new cache whenever packages or source files change.
-  key: ${{ runner.os }}-nextjs-${{ hashFiles('**/package-lock.json') }}-${{ hashFiles('**.[jt]sx?') }}
+  key: ${{ runner.os }}-nextjs-${{ hashFiles('**/package-lock.json') }}-${{ hashFiles('**.[jt]s', '**.[jt]sx') }}
   # If source files changed but packages didn't, rebuild from a prior cache.
   restore-keys: |
     ${{ runner.os }}-nextjs-${{ hashFiles('**/package-lock.json') }}-