Replace use of add-path

Replace use of add-path

Output from gha
The add-path command is deprecated and will be disabled soon. Please upgrade to using Environment Files. For more information see: https://github.blog/changelog/2020-10-01-github-actions-deprecating-set-env-and-add-path-commands/

.github/workflows/ResInsightWithCache.yml

@@ -100,8 +100,9 @@ jobs:
         run: New-Item ${{ env.BUILDCACHE_DIR }} -ItemType "directory" -Force 
         shell: pwsh
       - name: Add buildcache to system path
-        run: echo "::add-path::${{ github.workspace }}/bin"
-
+        run: echo "${{github.workspace}}/bin" | Out-File -FilePath $env:GITHUB_PATH -Encoding utf8
+        shell: pwsh
+        
       - name: Cache Qt        
         id: cache-qt
         uses: actions/cache@v2