Add regression tests for `deprecated_attribute()`
Add regression tests for `deprecated_attribute()`

The function `astropy.utils.decorators.deprecated_attribute()` ignores
its `message`, `alternative` and `pending` arguments. This commit
expands tests of that function so that the problem is revealed.

pllim/astropy,astropy/astropy,pllim/astropy,mhvk/astropy,larrybradley/astropy,mhvk/astropy,pllim/astropy,saimn/astropy,lpsinger/astropy,lpsinger/astropy,astropy/astropy,mhvk/astropy,astropy/astropy,StuartLittlefair/astropy,mhvk/astropy,larrybradley/astropy,StuartLittlefair/astropy,StuartLittlefair/astropy,saimn/astropy,saimn/astropy,lpsinger/astropy,saimn/astropy,larrybradley/astropy,lpsinger/astropy,StuartLittlefair/astropy,pllim/astropy,astropy/astropy,larrybradley/astropy,StuartLittlefair/astropy,mhvk/astropy,pllim/astropy,saimn/astropy,astropy/astropy,lpsinger/astropy,larrybradley/astropy