Testsuite: suppress spurious warnings under Octave 7

In this version of Octave, “warning on” really enables all warnings (while this
was not the case in Octave 6, suprisingly; I think this used to be different
with even older Octave releases).

src/@dseries/subsref.m

@@ -15,7 +15,7 @@ function r = subsref(o, S) % --*-- Unitary tests --*--
 %                     by applying a public method on `o`, or a dseries object built by extracting
 %                     a variable from `o`, or a dseries object containing a subsample.
 
-% Copyright © 2011-2021 Dynare Team
+% Copyright © 2011-2022 Dynare Team
 %
 % This file is part of Dynare.
 %
@@ -488,9 +488,9 @@ return
      t(2) = 0;
  end
  try
-     warning off all
+     warnstate = warning('off');
      c = ts1{'[A-Z]_1'};
-     warning on all
+     warning(warnstate);
      t(3) = 0;
  catch
      t(3) = 1;

tests/runalltests.m

 function runalltests()
 
-% Copyright © 2015-2019 Dynare Team
+% Copyright © 2015-2022 Dynare Team
 %
 % This code is free software: you can redistribute it and/or modify
 % it under the terms of the GNU General Public License as published by
@@ -40,7 +40,7 @@ catch
     initialize_dseries_class();
 end
 
-warning off
+warnstate = warning('off');
 
 if isoctave()
     if ~user_has_octave_forge_package('io')
@@ -60,7 +60,7 @@ else
     system('touch pass');
 end
 
-warning on
+warning(warnstate);
 path(opath);
 
 display_report(r);