Merge pull request #18994 from Wilfred/failed_rustc_cfg_as_warning

internal: Treat cfg fetching failures as a warning

Author: Veykril

src/tools/rust-analyzer/crates/project-model/src/toolchain_info/rustc_cfg.rs

@@ -19,7 +19,7 @@ pub fn get(
     let rustc_cfgs = match rustc_cfgs {
         Ok(cfgs) => cfgs,
         Err(e) => {
-            tracing::error!(?e, "failed to get rustc cfgs");
+            tracing::warn!(?e, "failed to get rustc cfgs");
             return vec![];
         }
     };