Rollup merge of #63560 - Centril:mv-generator-test, r=petrochenkov

move test that shouldn't be in test/run-pass/

We no longer test `src/test/run-pass/`; the proper way now is `// run-pass` in `src/test/ui/`

r? @petrochenkov

src/test/run-pass/generator/niche-in-generator.rs → src/test/ui/generator/niche-in-generator.rs

@@ -1,5 +1,7 @@
 // Test that niche finding works with captured generator upvars.
 
+// run-pass
+
 #![feature(generators)]
 
 use std::mem::size_of_val;