fix: ensuring consistent column names across invocations in output dataset

tests/x-platform/mx_getgroups.test.sas

@@ -21,6 +21,11 @@
   desc=groups were found,
   outds=work.test_results
 )
+%mp_assertcols(work.test1,
+  cols=groupuri groupname groupdesc,
+  test=ALL,
+  desc=check all columns exist
+)
 
 %mx_getgroups(outds=work.test2,user=%mf_getuser())
 
@@ -28,4 +33,9 @@
   iftrue=(%mf_nobs(work.test2)>0),
   desc=groups for current user were found,
   outds=work.test_results
+)
+%mp_assertcols(work.test2,
+  cols=groupuri groupname groupdesc,
+  test=ALL,
+  desc=check all columns exist
 )