add a test for simple static set that sets a variable to the value of another variable

Author: lovasoa

tests/sql_test_files/it_works_set_variable_to_other_variable.sql

@@ -0,0 +1,9 @@
+SET x = 42;
+SET y = $x;
+SET z = $y;
+select 'text' as component,
+    case $z 
+        when '42' then 'It works !'
+        else 'It failed ! Expected 42 but got ' || COALESCE($z, 'NULL')
+    end
+AS contents;