disable test-swift-docc.txt to unblock PR testing

rdar://91638258

Author: eeckstein

test-swift-docc/test-swift-docc.txt

@@ -3,3 +3,6 @@
 // RNU: rm -rf %S/Output
 // RUN: %{docc} convert %S/DocCTest/Sources/DocCTest/DocCTest.docc --output-path %S/Output
 // RUN: ls %S/Output
+
+// REQUIRES: rdar91638258
+