Keep plugging holes in the test to placate CI.

If this happens again, I'm going to change tack and make this
an `// only-linux` test or something along those lines.

Author: pnkfelix

src/test/ui/non-ice-error-on-worker-io-fail.rs

@@ -24,6 +24,7 @@
 // ignore-windows - this is a unix-specific test
 // ignore-emscripten - the file-system issues do not replicate here
 // ignore-wasm - the file-system issues do not replicate here
+// ignore-arm - the file-system issues do not replicate here, at least on armhf-gnu
 
 #![crate_type="lib"]