Rollup merge of #127752 - uweigand:s390x-miropt-update, r=Mark-Simulacrum

Ignore allocation bytes in one more mir-opt test

Following on PR #126502, add `rustc -Zdump-mir-exclude-alloc-bytes` to tests/mir-opt/dataflow-const-prop/aggregate_copy.rs as well to skip writing allocation bytes in MIR dumps.

Fixes #126261

Author: matthiaskrgr