xtask: fix interplay between fmt-on-save and xsync #2182

Job	Run time
build mdbook guide	1m 32s
build artifacts [x64-linux]	6m 0s
build and check docs [x64-windows]	9m 55s
build openhcl [aarch64-linux]	5m 35s
verify openhcl binary size [x64]	6m 22s
clippy [windows], unit tests [x64-windows]	12m 52s
clippy [linux, macos], unit tests [x64-linux]	8m 26s
build openhcl [x64-linux]	7m 50s
clippy [linux-musl, misc nostd], unit tests [x64-linux-musl]	7m 22s
unit tests [aarch64-windows]	8m 36s
build and check docs [x64-linux]	2m 46s
test flowey local backend	3m 8s
xtask fmt (linux)	2m 25s
build artifacts (not for VMM tests) [aarch64-windows]	5m 39s
build artifacts (for VMM tests) [aarch64-windows]	11m 43s
build artifacts (not for VMM tests) [x64-windows]	4m 56s
build artifacts (for VMM tests) [x64-windows]	11m 54s
build artifacts [aarch64-linux]	5m 35s
xtask fmt (windows)	8m 5s
run vmm-tests [aarch64-windows]	6m 4s
run vmm-tests [x64-windows-amd]	11m 35s
run vmm-tests [x64-linux]	3m 31s
run vmm-tests [x64-windows-intel]	10m 30s
openvmm checkin gates	9s
	2h 42m 30s

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