bugfix: add arg to write_line_break() in spack_yaml (#42727)

`ruamel`'s `Emitter.write_line_break()` method takes an extra argument that we forgot to
implement in our custom emitter.

lib/spack/spack/util/spack_yaml.py

@@ -296,8 +296,8 @@ def process_scalar(self):
         if marked(self.event.value):
             self.saved = self.event.value
 
-    def write_line_break(self):
-        super().write_line_break()
+    def write_line_break(self, data=None):
+        super().write_line_break(data)
         if self.saved is None:
             _ANNOTATIONS.append(colorize("@K{---}"))
             return