fix(test): remove workspace test build warnings

Drop the unused test-only import in fabro-server and the unused test
binding in fabro-workflow so workspace test builds stay warning-free.

lib/crates/fabro-server/src/server.rs

@@ -5854,8 +5854,6 @@ async fn get_graph(
 
 #[cfg(test)]
 mod tests {
-    use std::path::PathBuf;
-
     use super::*;
     use axum::body::Body;
     use axum::http::Request;

lib/crates/fabro-workflow/src/operations/start.rs

@@ -1026,7 +1026,7 @@ mod tests {
             ),
         ]));
 
-        let created = crate::operations::create(
+        crate::operations::create(
             &store,
             crate::operations::CreateRunInput {
                 workflow: crate::operations::WorkflowInput::Bundled(