github/workflows: fix cache key

.github/workflows/user_project_ci.yml

diff --git a/.github/workflows/user_project_ci.yml b/.github/workflows/user_project_ci.yml
index f6008f2..b2864f7 100644
--- a/.github/workflows/user_project_ci.yml
+++ b/.github/workflows/user_project_ci.yml
@@ -123,7 +123,7 @@
           verilog/rtl/user_module.ir
           verilog/rtl/user_module_opt.ir
           verilog/rtl/user_module.v
-        key: ${{ runner.os }}-${{ env.CACHE_NUMBER }}-rtl-${{ github.run_id }}
+        key: ${{ runner.os }}-${{ env.CACHE_KEY }}-rtl-${{ github.run_id }}
 
     - name: fetch verilog and build config
       run: |