chore: improve quickjs disabled error message, disable rust cache in CI

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

.github/workflows/backend-test.yml

@@ -75,7 +75,7 @@ jobs:
         working-directory: /
       - uses: actions-rust-lang/setup-rust-toolchain@v1
         with:
-          cache-workspaces: backend
+          cache: false
           toolchain: 1.90.0
       - name: Read EE repo commit hash
         run: |

backend/windmill-jseval/src/lib.rs

@@ -835,7 +835,7 @@ pub async fn eval_timeout_quickjs(
     _by_id: Option<&IdContext>,
     _ctx: Option<Vec<(String, String)>>,
 ) -> anyhow::Result<Box<RawValue>> {
-    anyhow::bail!("quickjs feature is not enabled")
+    anyhow::bail!("JavaScript expression evaluation requires the `quickjs` feature. Enable it with: cargo build --features quickjs")
 }
 
 #[cfg(not(feature = "quickjs"))]
@@ -843,7 +843,7 @@ pub async fn eval_simple_js(
     _expr: String,
     _globals: HashMap<String, serde_json::Value>,
 ) -> anyhow::Result<Box<RawValue>> {
-    anyhow::bail!("quickjs feature is not enabled")
+    anyhow::bail!("JavaScript expression evaluation requires the `quickjs` feature. Enable it with: cargo build --features quickjs")
 }
 
 // ── Tests ────────────────────────────────────────────────────────────