Auto merge of #87250 - robojumper:87199-sized-relaxation, r=nikomatsakis

Fix implicit Sized relaxation when attempting to relax other, unsupported trait

Fixes #87199.

Do note that this bug fix causes code like the `ref_arg::<[i32]>(&[5]);` line in the test case in combination with an affected function to no longer compile.

compiler/rustc_typeck/src/astconv/mod.rs

@@ -838,6 +838,7 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
                              this does nothing because the given bound is not \
                              a default; only `?Sized` is supported",
                         );
+                        return false;
                     }
                 }
             }