mesa: consider glPushMatrix a no-op change from the driver perspective

It doesn't change any states.

Reviewed-by: Adam Jackson <ajax@redhat.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/6946>

src/mesa/main/matrix.c

@@ -326,7 +326,6 @@ push_matrix(struct gl_context *ctx, struct gl_matrix_stack *stack,
                       &stack->Stack[stack->Depth] );
    stack->Depth++;
    stack->Top = &(stack->Stack[stack->Depth]);
-   ctx->NewState |= stack->DirtyFlag;
 }