patch fleets in 0802preview tag (#20713)

Author: FumingZhang

specification/containerservice/resource-manager/readme.md

@@ -45,6 +45,7 @@ These settings apply only when `--tag=package-preview-2022-08` is specified on t
 ``` yaml $(tag) == 'package-preview-2022-08'
 input-file:
   - Microsoft.ContainerService/preview/2022-08-02-preview/managedClusters.json
+  - Microsoft.ContainerService/preview/2022-07-02-preview/fleets.json
 ```
 
 ### Tag: package-2022-07