Add curation for gem diff-lcs

The correct license is (GPL-2.0-or-later OR Artistic-2.0 OR MIT) which can be found
at https://github.com/halostatue/diff-lcs/blob/bb28cd9c8e395cabb3a905cb651249133169b2e6/LICENCE.md

Author: ospo-bot

curations/gem/rubygems/-/diff-lcs.yaml

@@ -0,0 +1,9 @@
+coordinates:
+    type: gem
+    provider: rubygems
+    namespace: '-'
+    name: diff-lcs
+revisions:
+    1.6.1:
+        licensed:
+            declared: (GPL-2.0-or-later OR Artistic-2.0 OR MIT)