Rollup merge of rust-lang#158163 - xmakro:fix-variances-cycle-recovery-count, r=petrochenkov

Fix too-short variance slice in `variances_of` cycle recovery

This changes the cycle-error fallback in `variances_of` to size the slice the same way the provider does in [`variance/solve.rs:117`](https://github.com/rust-lang/rust/blob/32ea3615cc027bcb8fd720c7511ffb484f6223a3/compiler/rustc_hir_analysis/src/variance/solve.rs#L117).

This can otherwise ICE under the parallel frontend in `relate_args_with_variances` for items that inherit their generics from a parent (like a tuple struct constructor). See rust-lang#154560 (comment)

Author: jhpratt

compiler/rustc_query_impl/src/handle_cycle_error.rs

@@ -105,7 +105,7 @@ pub(crate) fn variances_of<'tcx>(
     err: Diag<'_>,
 ) -> &'tcx [ty::Variance] {
     let _guar = err.delay_as_bug();
-    let n = tcx.generics_of(def_id).own_params.len();
+    let n = tcx.generics_of(def_id).count();
     tcx.arena.alloc_from_iter(iter::repeat_n(ty::Bivariant, n))
 }