[Backport v3.0] Ignore MQTT test flake #6853

Job	Run time
Build Spin static (aarch64, aarch64-unknown-linux-musl)	16m 25s
Review new dependencies for known vulnerabilities	3s
Build Spin static (amd64, x86_64-unknown-linux-musl)	15m 17s
Build Spin Ubuntu	22m 2s
all-integration-tests	22m 50s
Build Spin (windows-latest)	32m 20s
Lint Rust	6m 26s
Run release build steps (ubuntu-20.04, amd64, --features openssl/vendored, target/release)	15m 11s
Build Spin (macos-13)	15m 17s
Test Spin (ubuntu-22.04-4core-spin)	8m 40s
Build Spin (macos-14)	9m 24s
Test Spin (macos-14)	24m 59s
Run release build steps (ubuntu-20.04, aarch64, --features openssl/vendored --target aarch64-unkn...	16m 24s
Run release build steps (macos-13, amd64, target/release)	29m 46s
Run release build steps (macos-14, aarch64, target/release)	13m 32s
Run release build steps (windows-latest, amd64, .exe, target/release)	27m 6s
	4h 35m 42s

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