Update CI workflow template to unpin from nightly explicitly, relying on foundry-toolchain default (#9573)

* default CI workflow template to stable as opposed to nightly, related: foundry-rs/foundry-toolchain#60

* remove pinning to stable in workflow file, rely on default in foundry-toolchain - now being nightly, becoming stable

Author: zerosnacks

crates/forge/assets/workflowTemplate.yml

@@ -22,8 +22,6 @@ jobs:
 
       - name: Install Foundry
         uses: foundry-rs/foundry-toolchain@v1
-        with:
-          version: nightly
 
       - name: Show Forge version
         run: |