Don't ask to make a HEX20 second_order=true

There's currently a bug in libMesh wherein if you ask to
`all_second_order()` a mesh, with `full_order=true`, it will
ignore existing second-but-not-full-order elements.  These tests were
relying on that buggy behavior.

Refs #26060 ... and hopefully fixes it; I'm still looking for other bad
tests elsewhere.

test/tests/mortar/continuity-3d-non-conforming/tests

@@ -17,7 +17,7 @@
     min_ad_size = 200
     input = 'continuity_sphere_hex.i'
     exodiff = 'continuity_sphere_hex20_out.e'
-    cli_args = 'Mesh/second_order=true Mesh/file/file=spheres_hex20.e Variables/T/order=SECOND '
+    cli_args = 'Mesh/file/file=spheres_hex20.e Variables/T/order=SECOND '
                'Outputs/file_base=continuity_sphere_hex20_out'
     requirement = 'The system shall be able to produce the expected result for a solution continuity '
                   'test case using the mortar method on a HEX20 mesh with curved geometry, e.g. the '
@@ -138,7 +138,7 @@
     type = 'Exodiff'
     input = 'continuity_penalty_sphere_hex.i'
     exodiff = 'continuity_penalty_sphere_hex20_out.e'
-    cli_args = 'Mesh/second_order=true Mesh/file/file=spheres_coarse_hex20.e Variables/T/order=SECOND '
+    cli_args = 'Mesh/file/file=spheres_coarse_hex20.e Variables/T/order=SECOND '
                'Outputs/file_base=continuity_penalty_sphere_hex20_out -pc_type lu'
     requirement = 'The system shall be able to produce the expected result for a solution continuity '
                   'test case using the penalty-based mortar method on a HEX20 mesh with curved '
@@ -152,7 +152,7 @@
     type = 'Exodiff'
     input = 'continuity_penalty_sphere_hex.i'
     exodiff = 'continuity_penalty_sphere_hex20_out.e'
-    cli_args = 'Mesh/second_order=true Mesh/file/file=spheres_coarse_hex20.e Variables/T/order=SECOND '
+    cli_args = 'Mesh/file/file=spheres_coarse_hex20.e Variables/T/order=SECOND '
                'Constraints/mortar/type=ADPenaltyEqualValueConstraint Outputs/file_base=continuity_penalty_sphere_hex20_out -pc_type lu'
     requirement = 'The system shall be able to produce the same result using the penalty-based '
                   'mortar method with and without automatic differentiation.'