fix assignment

action.yml

@@ -40,7 +40,7 @@ runs:
           commitish: ${{ inputs.cog-commitish }}
 
       - name: Download an existing Cog version
-        if: ${{ inputs.cog-commitish = '' }}
+        if: ${{ inputs.cog-commitish == '' }}
         shell: bash
         run: |
           sudo curl -o /usr/local/bin/cog -L https://github.com/replicate/cog/releases/download/${{ inputs.cog-version }}/cog_Linux_x86_64