chore: bump the rustfmt nightly to nightly-2026-08-23 (#1267)

* chore: bump the rustfmt nightly to nightly-2026-08-23

* chore: bump the rustfmt nightly in the pre-commit hooks

The hooks name the toolchain in their own entry line, which the workflow
environment does not reach, so both carry the version and both have to move.

Author: lfrancke

.github/workflows/pr_prek.yaml

@@ -7,7 +7,7 @@ on:
 
 env:
   CARGO_TERM_COLOR: always
-  RUST_TOOLCHAIN_VERSION: "nightly-2026-07-01"
+  RUST_TOOLCHAIN_VERSION: "nightly-2026-08-23"
 
 permissions: {}
 

.pre-commit-config.yaml

@@ -67,7 +67,7 @@ repos:
         name: cargo-rustfmt
         language: system
         # Pinning to a specific rustc version, so that we get consistent formatting
-        entry: cargo +nightly-2026-07-01 fmt --all -- --check
+        entry: cargo +nightly-2026-08-23 fmt --all -- --check
         stages: [pre-commit, pre-merge-commit]
         pass_filenames: false
         files: \.rs$