fix(ci): Work around binary distribution tool bug

The binary distribution tool we use, `dist`, seems to ignore `RUSTFLAGS`
set in `.cargo/config.toml`. See also:
axodotdev/cargo-dist#1571

Using a custom build setup, it is possible to patch `RUSTFLAGS`. This is
considered a temporary patch, until the underlying bug in `dist` is
fixed. See also:
https://opensource.axo.dev/cargo-dist/book/ci/customizing.html

changelog: ignore

.github/workflows/build-workaround

@@ -0,0 +1,6 @@
+# A workaround for
+# https://github.com/axodotdev/cargo-dist/issues/1571
+# using
+# https://opensource.axo.dev/cargo-dist/book/ci/customizing.html#customizing-build-setup
+- name: Update RUSTFLAGS with --cfg tokio_unstable
+  run: echo RUSTFLAGS="$RUSTFLAGS --cfg tokio_unstable" >> "$GITHUB_ENV"

.github/workflows/release.yml

@@ -119,6 +119,8 @@ jobs:
       - uses: actions/checkout@v4
         with:
           submodules: recursive
+      - name: "Update RUSTFLAGS with --cfg tokio_unstable"
+        run: "echo RUSTFLAGS=\"$RUSTFLAGS --cfg tokio_unstable\" >> \"$GITHUB_ENV\""
       - name: Install dist
         run: ${{ matrix.install_dist }}
       # Get the dist-manifest

dist-workspace.toml

@@ -17,3 +17,4 @@ install-path = "CARGO_HOME"
 install-updater = true
 # Whether to enable GitHub Attestations
 github-attestations = true
+github-build-setup = "build-workaround"