[red-knot] Shorten the paths for some mdtest files (#14267)

crates/red_knot_python_semantic/resources/mdtest/annotations/string.md

@@ -0,0 +1,9 @@
+# String annotations
+
+```py
+def f() -> "int":
+    return 1
+
+# TODO: We do not support string annotations, but we should not panic if we encounter them
+reveal_type(f())  # revealed: @Todo
+```