megatest: make it green on Linux

tests/generics/tgenerics_issues.nim

@@ -24,12 +24,11 @@ G:0,1:0.1
 G:0,1:0.1
 H:1:0.1
 '''
+joinable: false
 """
 
-
 import macros, sequtils, sets, sugar, tables, typetraits
 
-
 block t88:
   type
     BaseClass[V] = object of RootObj

tests/generics/tgenerics_various.nim

@@ -5,12 +5,11 @@ direct
 generic
 generic
 '''
+joinable: false
 """
 
-
 import algorithm, sugar, sequtils, typetraits, asyncdispatch
 
-
 block tconfusing_arrow:
   type Deck = object
     value: int

tests/generics/tparser_generator.nim

@@ -1,6 +1,7 @@
 discard """
   output: '''Match failed: spam
 Match failed: ham'''
+joinable: false
 """
 
 # bug #6220