bench: Update pinned nightly to 2026-05-23

[tgross35]

Advance to after the first regression in hypot but before the second regression. See 1 for context on the regression.

ci: allow-regressions

[rustbot]

This PR was rebased onto a different main commit. Here's a range-diff highlighting what actually changed.

Rebasing is a normal part of keeping PRs up to date, so no action is needed—this note is just to help reviewers.

[tgross35]

Aarch64

58
icount::icount_bench_math_group::icount_bench_hypot logspace:(setup_hypot())
  Baselines:                   arch_enabled|arch_enabled (old)
  Instructions:                       19914|18946                (+5.10926%) [+1.05109x]
  L1 Hits:                            21327|20360                (+4.74951%) [+1.04750x]
  LL Hits:                                1|1                    (No change)
  RAM Hits:                              16|15                   (+6.66667%) [+1.06667x]
  Total read+write:                   21344|20376                (+4.75069%) [+1.04751x]
  Estimated Cycles:                   21892|20890                (+4.79655%) [+1.04797x]
Performance has regressed: Instructions (18946 -> 19914) regressed by +5.10926% (>+5.00000%)

i686

icount::icount_bench_math_group::icount_bench_hypot logspace:(setup_hypot())
  Baselines:                   arch_enabled|arch_enabled (old)
  Instructions:                      195326|192906               (+1.25450%) [+1.01254x]
  L1 Hits:                           265396|262983               (+0.91755%) [+1.00918x]
  LL Hits:                               12|5                    (+140.000%) [+2.40000x]
  RAM Hits:                              71|71                   (No change)
  Total read+write:                  265479|263059               (+0.91995%) [+1.00920x]
  Estimated Cycles:                  267941|265493               (+0.92206%) [+1.00922x]

x86-64

[259](https://github.com/rust-lang/compiler-builtins/actions/runs/31163036146/job/92817735883?pr=1250#step:7:6259)
icount::icount_bench_math_group::icount_bench_hypot logspace:(setup_hypot())
  Baselines:                   arch_enabled|arch_enabled (old)
  Instructions:                       40337|38446                (+4.91859%) [+1.04919x]
  L1 Hits:                            53115|51224                (+3.69163%) [+1.03692x]
  LL Hits:                                3|3                    (No change)
  RAM Hits:                              35|35                   (No change)
  Total read+write:                   53153|51262                (+3.68889%) [+1.03689x]
  Estimated Cycles:                   54355|52464                (+3.60438%) [+1.03604x]

All expected, #1249

Some other small improvements < 1%