ci: skip host rustup for mipsel-softfloat (docker handles its toolchain)

v1.1.0 CI run (24820831905) failed at the dtolnay/rust-toolchain@stable
step for the mipsel-unknown-linux-musl matrix entry: that target is
tier-3 in stable Rust and `rust-std` isn't available via rustup, so
the `targets:` parameter errors out with

    error: component 'rust-std' for target 'mipsel-unknown-linux-musl'
    is unavailable for download

before the docker step that actually builds it ever runs. The docker
image we use (`messense/rust-musl-cross:mipsel-musl-softfloat`) bundles
its own Rust + std, so the host-level rustup isn't needed here at all.

Gated by `matrix.mipsel_softfloat != true` so the other 8 targets still
install their toolchain the normal way. `continue-on-error: true` on
the job level already prevented this from blocking the release, but
the failure was noisy and confusing — fix makes the whole matrix green.

Pushed as a small follow-up to v1.1.0 so the re-tag picks it up.

.github/workflows/release.yml

@@ -66,7 +66,16 @@ jobs:
     steps:
       - uses: actions/checkout@v4
 
+      # Skip the host-level rustup install for mipsel-softfloat — that
+      # target is tier-3 in stable Rust (no prebuilt stdlib available
+      # via rustup), and the docker image we use for this build ships
+      # its own Rust toolchain + std. Trying to pass
+      # `targets: mipsel-unknown-linux-musl` to dtolnay/rust-toolchain
+      # errors out with "error: component 'rust-std' for target
+      # 'mipsel-unknown-linux-musl' is unavailable for download", which
+      # fails the job before the docker step ever runs.
       - uses: dtolnay/rust-toolchain@stable
+        if: matrix.mipsel_softfloat != true
         with:
           targets: ${{ matrix.target }}