Not any more. :) They were variant spellings way back in Middle English (roughly Norman conquest to 1500) when they split off from the French root.
Ordnance now means of military, guns and armaments (cf Ordnance Survey)
Ordinance means an order or religious rite (and apparently bylaw in the US)
Some of it is [0].
This fact is ever more important in the age of AI.
https://www.thefreedictionary.com/ordnance
Also: https://www.etymonline.com/word/ordnance
"Ordnance" seems to be the more conventional spelling for this meaning, but I'm not sure that makes it uniquely correct. Linguistics isn't an exact science.