Use geodiff 0.8.8 for both linux & windows build

Author: wonder-sk

.github/workflows/linux.yml

@@ -24,7 +24,7 @@ jobs:
       - name: Checkout geodiff
         uses: actions/checkout@v2
         with:
-          ref: 0.8.6
+          ref: 0.8.8
           repository: lutraconsulting/geodiff
           path: geodiff
 

.github/workflows/windows.yml

@@ -27,7 +27,7 @@ jobs:
       - name: Checkout geodiff
         uses: actions/checkout@v2
         with:
-          ref: master
+          ref: 0.8.8
           repository: lutraconsulting/geodiff
           path: geodiff