ci: solidity better caching (#410)

Since we introduced the `abis` job we have to be completely sure the
cache contains the latest solidity changes.
Otherwise it will always exit with errors, as the head commit contains
the latest abi bindings, but the `abis` job generates abis based on
outdated solidity files.

.github/workflows/solidity.yml

@@ -20,6 +20,8 @@ defaults:
 jobs:
   init:
     runs-on: ubuntu-latest
+    outputs:
+      cache-key: ${{ steps.set-cache-key.outputs.cache-key }}
     strategy:
       fail-fast: true
 
@@ -30,6 +32,10 @@ jobs:
       - name: Install Foundry
         uses: foundry-rs/foundry-toolchain@v1
 
+      - name: Set cache key
+        id: set-cache-key
+        run: echo "cache-key=ci-solidity-${{ hashFiles('**/*.sol') }}" >> "$GITHUB_OUTPUT"
+
       - name: Install dependencies
         run: forge soldeer update
 
@@ -40,16 +46,16 @@ jobs:
         uses: actions/cache/save@v4
         with:
           path: contracts
-          key: ci-solidity-${{ github.ref }}
+          key: ${{ steps.set-cache-key.outputs.cache-key }}
 
       - id: forge
-        run: echo "FORGE_PATH=$(which forge)" >> $GITHUB_OUTPUT
+        run: echo "forge_path=$(which forge)" >> "$GITHUB_OUTPUT"
 
       - name: Upload forge
         uses: actions/upload-artifact@v4
         with:
           name: forge
-          path: ${{ steps.forge.outputs.FORGE_PATH }}
+          path: ${{ steps.forge.outputs.forge_path }}
 
   test:
     needs: init
@@ -59,7 +65,7 @@ jobs:
         uses: actions/cache/restore@v4
         with:
           path: contracts
-          key: ci-solidity-${{ github.ref }}
+          key: ${{ needs.init.outputs.cache-key }}
 
       - name: Restore forge
         uses: actions/download-artifact@v4
@@ -80,7 +86,7 @@ jobs:
         uses: actions/cache/restore@v4
         with:
           path: contracts
-          key: ci-solidity-${{ github.ref }}
+          key: ${{ needs.init.outputs.cache-key }}
 
       - name: Restore forge
         uses: actions/download-artifact@v4
@@ -101,7 +107,7 @@ jobs:
         uses: actions/cache/restore@v4
         with:
           path: contracts
-          key: ci-solidity-${{ github.ref }}
+          key: ${{ needs.init.outputs.cache-key }}
 
       - name: Restore forge
         uses: actions/download-artifact@v4
@@ -135,7 +141,7 @@ jobs:
         uses: actions/cache/restore@v4
         with:
           path: contracts
-          key: ci-solidity-${{ github.ref }}
+          key: ${{ needs.init.outputs.cache-key }}
 
       - name: Restore forge
         uses: actions/download-artifact@v4