rustup: update to `nightly-2025-06-23` (~1.89). #639

Job	Run time
Test (macOS-latest)	7m 59s
Test (ubuntu-24.04)	8m 22s
Compiletest (windows-2022)	16m 31s
Android (ubuntu-24.04, aarch64-linux-android)	8m 28s
Difftest (macOS-latest)	9m 28s
Test (windows-2022)	14m 45s
Compiletest (ubuntu-24.04)	8m 52s
Compiletest (macOS-latest)	7m 15s
Lint	5m 19s
Difftest (windows-2022)	17m 14s
cargo-deny	1m 29s
Difftest (ubuntu-24.04)	10m 14s
test_success	4s
	1h 56m 0s

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