Attempt to unbreak CI (Android / libc 0.2.127).

Author: eddyb

.github/workflows/ci.yaml

@@ -94,7 +94,8 @@ jobs:
           echo "::endgroup::"
 
           echo "::group::Install cargo-apk"
-          cargo install cargo-apk
+          echo "FIXME(eddyb) working around libc 0.2.127 breakage by using stable Rust!"
+          cargo +stable install cargo-apk
           echo "::endgroup::"
 
           echo "::group::Add aarch64-linux-android target"