pypy: enable dbm support in db dependency

fixes test breakage introduced by #21049 dca3a4e3f4

pkgs/top-level/all-packages.nix

@@ -5880,6 +5880,7 @@ with pkgs;
   pypy27 = callPackage ../development/interpreters/python/pypy/2.7 {
     self = pypy27;
     python = python27.override{x11Support=true;};
+    db = db.override { dbmSupport = true; };
   };
 
   python2nix = callPackage ../tools/package-management/python2nix { };