Ignore unstable key when overriding config

src/test/mod.rs

@@ -500,7 +500,7 @@ fn read_config(filename: &Path) -> Config {
     };
 
     for (key, val) in &sig_comments {
-        if key != "target" && key != "config" {
+        if key != "target" && key != "config" && key != "unstable" {
             config.override_value(key, val);
             if config.is_default(key) {
                 warn!("Default value {} used explicitly for {}", val, key);

tests/config/normalize_multiline_doc_attribute.toml

@@ -1 +0,0 @@
-normalize_doc_attributes = true

tests/source/normalize_multiline_doc_attribute.rs

@@ -1,4 +1,5 @@
 // rustfmt-unstable: true
+// rustfmt-normalize_doc_attributes: true
 
 #[doc = "This comment
 is split

tests/target/normalize_multiline_doc_attribute.rs

@@ -1,4 +1,5 @@
 // rustfmt-unstable: true
+// rustfmt-normalize_doc_attributes: true
 
 ///This comment
 ///is split