chore: pin nim version in CI

Author: kevaundray

.github/workflows/test-nim-bindings.yml

@@ -32,6 +32,7 @@ jobs:
         uses: jiro4989/setup-nim-action@v1
         with:
           repo-token: ${{ secrets.GITHUB_TOKEN }}
+          nim-version: '2.0.4'
 
       - name: Test Nim project
         working-directory: bindings/nim/nim_code