Re-add bounds to megaparsec and mmark as megaparsec causes name clashes (#3159)

build-constraints.yaml

@@ -3169,6 +3169,10 @@ packages:
         # section as wreq-0.5.2 makes tests compile properly
         - wreq < 0.5.2
 
+        # https://github.com/fpco/stackage/issues/3159
+        - megaparsec < 6.4
+        - mmark < 0.0.4.1
+
 # end of packages
 
 # Package flags are applied to individual packages, and override the values of