Try to fix ghcup cache in CI via sudo chmod

Author: Mikolaj

.github/workflows/validate.yml

@@ -57,6 +57,11 @@ jobs:
 
       - uses: actions/checkout@v3
 
+      - name: Sudo chmod to permit ghcup to update its cache
+        run: |
+          sudo mkdir /usr/local/.ghcup
+          sudo chmod -R g+wr /usr/local/.ghcup
+
       - uses: haskell/actions/setup@v2
         id: setup-haskell
         with: