libct/cg/fs: don't write cpu_burst twice on ENOENT #5993

Job	Run time
cross-i386	1m 24s
cross-i386 (runc_nodmz)	1m 33s
test (ubuntu-20.04, 1.20.x, rootless, -race)	6m 21s
test (ubuntu-20.04, 1.20.x, rootless)	6m 12s
test (ubuntu-20.04, 1.20.x, -race)	7m 7s
test (ubuntu-20.04, 1.20.x)	6m 27s
test (ubuntu-20.04, 1.21.x, rootless, -race)	6m 9s
test (ubuntu-20.04, 1.21.x, rootless)	6m 22s
test (ubuntu-20.04, 1.21.x, -race)	7m 17s
test (ubuntu-20.04, 1.21.x)	6m 16s
test (ubuntu-20.04, 1.21.x, criu-dev)	6m 57s
test (ubuntu-22.04, 1.20.x, rootless, -race)	10m 2s
test (ubuntu-22.04, 1.20.x, rootless)	10m 17s
test (ubuntu-22.04, 1.20.x, -race)	8m 55s
test (ubuntu-22.04, 1.20.x)	8m 7s
test (ubuntu-22.04, 1.21.x, rootless, -race)	10m 11s
test (ubuntu-22.04, 1.21.x, rootless)	9m 46s
test (ubuntu-22.04, 1.21.x, -race)	8m 30s
test (ubuntu-22.04, 1.21.x)	7m 45s
test (ubuntu-22.04, 1.21.x, runc_nodmz)	7m 52s
test (ubuntu-22.04, 1.21.x, criu-dev)	8m 6s
test (actuated-arm64-6cpu-8gb, 1.21.x, rootless)	10m 55s
test (actuated-arm64-6cpu-8gb, 1.21.x)	7m 15s
	2h 49m 46s

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