ci(windows): force ~/.cargo/bin onto GITHUB_PATH after binstall

Windows ci.yml run 24929261378 (commit 0889fbb) failed at `Run just ci`
with `just: command not found` despite cargo-binstall logging
"v1.50.0 is already installed". Root cause: the rustup-init step's
`echo $CARGO_HOME\bin >> $GITHUB_PATH` line is gated behind
`command -v rustup`, which always succeeds on windows-latest (rustup
pre-installed). When Swatinem rust-cache partial-restores ~/.cargo/bin
containing a previously-installed just.exe, binstall skips install AND
its PATH side-effect — leaving bash steps unable to find just.exe even
though it's on disk.

Forcing $env:GITHUB_PATH after binstall is unconditional and idempotent.
Reverts to the prior latent-flakiness state if the upstream rustup-init
gate is fixed.

Independent of the fuzz/bench fixes in 0889fbb — that commit only
modified fuzz.yml + 2 Cargo.toml files; the Windows breakage was a
pre-existing race that finally hit on this push's cache-state shuffle.

Author: utof

.github/workflows/ci.yml

@@ -67,6 +67,18 @@ jobs:
           Invoke-WebRequest -Uri "https://github.com/cargo-bins/cargo-binstall/releases/latest/download/cargo-binstall-x86_64-pc-windows-msvc.zip" -OutFile binstall.zip
           Expand-Archive binstall.zip -DestinationPath "$env:USERPROFILE\.cargo\bin" -Force
           cargo binstall --no-confirm --locked just cargo-deny typos-cli cargo-nextest
+          # WHY explicit GITHUB_PATH update (added 2026-04-25): when
+          # Swatinem rust-cache partial-restores `~/.cargo/bin` containing
+          # a previously-installed just.exe, cargo-binstall logs "already
+          # installed" and SKIPS — including the side-effect PATH inject
+          # that fresh installs perform. Meanwhile rustup-init's
+          # `echo $CARGO_HOME\bin >> $GITHUB_PATH` is gated behind
+          # `command -v rustup`, which always succeeds on windows-latest
+          # (rustup is pre-installed). Net effect: bash steps that run
+          # `just ci` later can't see just.exe on PATH even though it's on
+          # disk. Forcing the GITHUB_PATH update here is unconditional and
+          # idempotent. Reproduced on ci.yml run 24929261378 (0889fbb).
+          "$env:USERPROFILE\.cargo\bin" | Out-File -FilePath $env:GITHUB_PATH -Append -Encoding utf8
 
       - uses: actions/setup-node@v4
         with: