Fix docstring test for static modeling language.

Author: ztangent

test/dsl/static_dsl.jl

@@ -558,9 +558,16 @@ trace, = generate(foo, (), constraints)
 end
 
 @testset "docstrings" begin
-    io = IOBuffer()
-    print(io, @doc model)
-    @test String(take!(io)) == "my documentation\n"
+    function doc_to_str(doc)
+        if doc isa Base.Docs.DocStr
+            # Handle @doc behavior in Julia 1.11 when REPL is not loaded
+            return doc.text[1]
+        else
+            # Handle pre-Julia 1.11 behavior of @doc
+            return strip(string(doc))
+        end
+    end
+    @test doc_to_str(@doc(model)) == "my documentation\n"
 end
 
 @testset "one-line definitions" begin