Making contains method case insenstive

[germa89]

As the title.

So we can do:

mapdl.parameters["mypar"] = 1234
assert "mypar" in mapdl.parameters # True
assert "MYPAR" in mapdl.parameters # True also

[codecov]

Codecov Report

Merging #2039 (29305dc) into main (a25fa9e) will increase coverage by 1.01%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##             main    #2039      +/-   ##
==========================================
+ Coverage   82.98%   83.99%   +1.01%     
==========================================
  Files          44       45       +1     
  Lines        7932     7933       +1     
==========================================
+ Hits         6582     6663      +81     
+ Misses       1350     1270      -80     

[clatapie]

LGTM!