Fix incorrect gutter bail message (#7534)

helix-view/src/editor.rs

@@ -611,7 +611,9 @@ impl std::str::FromStr for GutterType {
             "spacer" => Ok(Self::Spacer),
             "line-numbers" => Ok(Self::LineNumbers),
             "diff" => Ok(Self::Diff),
-            _ => anyhow::bail!("Gutter type can only be `diagnostics` or `line-numbers`."),
+            _ => anyhow::bail!(
+                "Gutter type can only be `diagnostics`, `spacer`, `line-numbers` or `diff`."
+            ),
         }
     }
 }