bake: fix output handling for push #3588

Job	Run time
prepare-binaries	4s
test-unit (ubuntu-22.04)	49s
buildkit-edge	1m 27s
test-unit (macos-12)	3m 16s
test-unit (windows-2022)	5m 46s
prepare-test-integration	2m 17s
binaries (darwin/amd64)	1m 26s
binaries (darwin/arm64)	1m 33s
binaries (linux/amd64)	1m 28s
binaries (linux/arm/v6)	1m 41s
binaries (linux/arm/v7)	1m 48s
binaries (linux/arm64)	1m 29s
binaries (linux/ppc64le)	1m 36s
binaries (linux/riscv64)	1m 37s
binaries (linux/s390x)	1m 37s
binaries (windows/amd64)	1m 35s
binaries (windows/arm64)	1m 37s
test-integration (docker, ./tests)	5m 43s
test-integration (docker\+containerd, ./tests)	4m 55s
test-integration (docker-container, ./tests)	2m 55s
test-integration (remote, ./tests)	3m 15s
release	16s
bin-image	0s
	48m 10s

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