Add a test for multiple &nil blocks/mixing them

Author: Earlopain

config.yml

@@ -4065,6 +4065,9 @@ nodes:
           - on error: NoKeywordsParameterNode
           # On parsing error of `f(..., ...)`, the first forwarding parameter is moved here:
           - on error: ForwardingParameterNode
+          # On parsing error of `f(&nil, &foo)`/`f(&foo, &nil)`, the first forwarding parameter is moved here:
+          - on error: BlockParameterNode
+          - on error: NoBlockParameterNode
       - name: keywords
         type: node[]
         kind:

test/prism/errors/4.1/multiple_blocks.txt

@@ -0,0 +1,12 @@
+def foo(&nil, &nil); end
+              ^ unexpected parameter order
+              ^~~~ multiple block parameters; only one block is allowed
+
+def foo(&foo, &nil); end
+              ^ unexpected parameter order
+              ^~~~ multiple block parameters; only one block is allowed
+
+def foo(&nil, &foo); end
+              ^ unexpected parameter order
+              ^~~~ multiple block parameters; only one block is allowed
+