[Super errors] Tweak warning indentation (#4567)

Author: chenglou

jscomp/super_errors/super_warnings.ml

@@ -6,7 +6,7 @@ let message (warning : Warnings.t)  =
   | Partial_match "" ->
       "You forgot to handle a possible case here, though we don't have more information on the value."
   | Partial_match s ->
-      "You forgot to handle a possible case here, for example: \n" ^ s
+      "You forgot to handle a possible case here, for example: \n  " ^ s
   | Unerasable_optional_argument ->
       String.concat ""
         ["This optional parameter in final position will, in practice, not be optional.\n";

lib/4.06.1/unstable/js_compiler.ml

@@ -411742,7 +411742,7 @@ let message (warning : Warnings.t)  =
   | Partial_match "" ->
       "You forgot to handle a possible case here, though we don't have more information on the value."
   | Partial_match s ->
-      "You forgot to handle a possible case here, for example: \n" ^ s
+      "You forgot to handle a possible case here, for example: \n  " ^ s
   | Unerasable_optional_argument ->
       String.concat ""
         ["This optional parameter in final position will, in practice, not be optional.\n";

lib/4.06.1/unstable/js_refmt_compiler.ml

@@ -571838,7 +571838,7 @@ let message (warning : Warnings.t)  =
   | Partial_match "" ->
       "You forgot to handle a possible case here, though we don't have more information on the value."
   | Partial_match s ->
-      "You forgot to handle a possible case here, for example: \n" ^ s
+      "You forgot to handle a possible case here, for example: \n  " ^ s
   | Unerasable_optional_argument ->
       String.concat ""
         ["This optional parameter in final position will, in practice, not be optional.\n";

lib/4.06.1/whole_compiler.ml

@@ -436831,7 +436831,7 @@ let message (warning : Warnings.t)  =
   | Partial_match "" ->
       "You forgot to handle a possible case here, though we don't have more information on the value."
   | Partial_match s ->
-      "You forgot to handle a possible case here, for example: \n" ^ s
+      "You forgot to handle a possible case here, for example: \n  " ^ s
   | Unerasable_optional_argument ->
       String.concat ""
         ["This optional parameter in final position will, in practice, not be optional.\n";