Tighten `str-to-string-128690.rs``CHECK{,-NOT}`s to make it less likely to incorrectly fail with symbol name mangling
The `invoke` to match on to `CHECK` or `CHECK-NOT` (latest master) looks like
```llvm
%_0.i.i.i.i.i.i.i.i.i.i.i.i.i1.i = invoke noundef zeroext i1 ``@"_ZN42_$LT$str$u20$as$u20$core..fmt..Display$GT$3fmt17ha18033e7fb4f14fcE"(ptr`` noalias noundef nonnull readonly align 1 %_3.val.i.i.i.i.i.i.i.i.i.i.i.i.i, i64 noundef %_3.val1.i.i.i.i.i.i.i.i.i.i.i.i.i, ptr noalias noundef nonnull align 8 dereferenceable(64) %formatter.i)
to label %bb1.i unwind label %cleanup.i, !noalias !80
```
in the local `.ll` output.
This test incorrectly failed in https://github.com/rust-lang/rust/pull/137483#issuecomment-2676925819 due to
```
// CHECK-NOT: {{(call|invoke).*}}fmt
```
matching against the unrelated call
```llvm
tail call void ``@_RNvNtCseLfmtnDCoTB_5alloc7raw_vec12handle_error``
```
It's not pretty by any means, but...
r? ``@saethlin``
e66fcc3410