allow srtree-3 (folivetti/srtree#21)

Author: juhp

build-constraints.yaml

@@ -5230,7 +5230,7 @@ packages:
     "Fabricio Olivetti de Franca <fabricio.olivetti@gmail.com> @folivetti":
         - hegg # dep of pandoc-symreg
         - pandoc-symreg
-        - srtree < 3 # https://github.com/folivetti/srtree/issues/21
+        - srtree
 
     "Eugen Wissner <belka@caraus.de> @belka-ew":
         - graphql