rustup: update to `nightly-2025-06-23` (~1.89). #647

Job	Run time
Android (ubuntu-24.04, aarch64-linux-android)	3m 3s
Test (ubuntu-24.04)	2m 59s
Test (macOS-latest)	2m 59s
Test (windows-2022)	2m 59s
Difftest (windows-2022)	2m 1s
Compiletest (windows-2022)	2m 57s
Compiletest (macOS-latest)	1m 41s
Lint	1m 0s
Difftest (macOS-latest)	1s
Compiletest (ubuntu-24.04)	3m 5s
Difftest (ubuntu-24.04)	1m 59s
cargo-deny	56s
test_success	3s
	25m 43s

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