Add stderr output

testsuite/tests/typecheck/should_run/T7861.stderr

- 
\ No newline at end of file
+T7861: T7861.hs:11:5:
+    Couldn't match type ‛a’ with ‛[a0]’
+      ‛a’ is a rigid type variable bound by
+          the type signature for f :: A a -> a at T7861.hs:10:6
+    Expected type: A a -> a
+      Actual type: A a0 -> [a0]
+    Relevant bindings include f :: A a -> a (bound at T7861.hs:11:1)
+    In the expression: doA
+    In an equation for ‛f’: f = doA
+(deferred type error)