test: add test cases for boolean columns

Author: yoRyuuuuu

internal/endtoend/testdata/emit_pointers_for_null_types/mysql/go/models.go

@@ -0,0 +1,11 @@
+CREATE table dt_boolean (
+  a boolean,
+  b bool,
+  c tinyint(1)
+);
+
+CREATE table dt_boolean_not_null (
+  a boolean not null,
+  b bool not null,
+  c tinyint(1) not null
+);