Fix Android CI and flaky GATT notification test

[colemancda]

Fixes the CI failures present on master.

Android (aarch64, build) — never passed since it was introduced

This job failed on every historical run, for two stacked reasons:

1. swift.org relocated the official Android SDK artifact, so the android/…_android-0.1.artifactbundle.tar.gz URL returned 404 and the job died at install.
2. With the URL corrected, the build then failed with 'semaphore.h' file not found. The official bundle declares sdkRootPath: "ndk-sysroot" but ships no sysroot of its own — it requires a separately installed Android NDK. The x86_64 job gets away with it because swift-android-action installs and wires up the NDK; a bare swift sdk install in a plain toolchain container does not.

Rather than add NDK provisioning, both ARM cross-compile jobs now share finagolfin's 6.1.3 SDK — the configuration the armv7 job has been passing with all along, since that bundle includes its own sysroot. The two jobs are collapsed into one matrix; the check names Android (aarch64, build) and Android (armv7, build) are unchanged.

Android (x86_64, test)

swift-test-flags: --no-parallel is passed verbatim to the on-device test runner binaries, and the XCTest runner rejects it (Error: Invalid option "--no-parallel"), failing the job before any test ran. Removed the flag; the race it guarded against is fixed at the source instead (below). Verified the job is genuinely green rather than vacuously green: the swift-testing invocation runs 474 tests in 30 suites, all passing.

Linux (swift:6.1.2, debug) — flaky GATTTests.notification()

The test slept a fixed 1 ms after server.writeValue before asserting, but notifications are delivered via detached tasks, so under CI load the assertion ran before delivery (receivedNotifications → []). Replaced the sleep with the same 10 ms/~5 s polling pattern already used for write completion in GATTClientServerTests.

---

Verified: swift test --filter GATTTests passes locally; the relocated SDK URL downloads with a checksum matching the existing value; the SDK bundle's swift-sdk.json was inspected directly to confirm the missing sysroot and the available target triples.

[github-code-quality]

Code Coverage Overview

Languages: Swift

Swift / code-coverage/llvm-cov

The overall coverage remains at 88%, unchanged from the master branch.

---

_{Updated July 20, 2026 03:55 UTC
Code Coverage is in Public Preview. Learn more and provide us with your feedback.}