Fix comment wandering left inside instance decls

src-literatetests/10-tests.blt

@@ -1065,6 +1065,13 @@ type ((a :+: b) c) = (a, c)
 instance MyClass Int where
   myMethod x = x + 1
 
+#test simple-method-comment
+
+instance MyClass Int where
+  myMethod x =
+    -- insightful comment
+    x + 1
+
 #test simple-method-signature
 
 instance MyClass Int where

src/Language/Haskell/Brittany/Internal/Layouters/Decl.hs

@@ -858,6 +858,7 @@ layoutClsInst :: ToBriDoc ClsInstDecl
 layoutClsInst lcid@(L _ cid) = docLines
   [ layoutInstanceHead
   , docEnsureIndent BrIndentRegular
+  $  docSetIndentLevel
   $  docSortedLines
   $  fmap layoutAndLocateSig          (cid_sigs cid)
   ++ fmap layoutAndLocateBind         (bagToList $ cid_binds cid)