👷 ci: read the toolchain under bash on every runner

The Windows wheel jobs run steps through PowerShell, which rejects the heredoc.
Resolve the version already names bash for the same reason.

Author: gaborbernat

.github/workflows/dist.yaml

@@ -85,6 +85,7 @@ jobs:
           echo "CIBW_MUSLLINUX_${ARCH^^}_IMAGE=$musllinux" >> "$GITHUB_ENV"
       - name: Read the toolchain rustup should install
         id: rust
+        shell: bash
         run: |
           python3 - <<'EOF' >> "$GITHUB_OUTPUT"
           import tomllib