[cmd/opampsupervisor] Fix leaks in e2e tests #31190

Job	Run time
collector-build	5m 10s
docker-build	5m 26s
supervisor-test	45s
kubernetes-test-matrix (v1.26.0, receiver/k8sclusterreceiver)	4m 41s
kubernetes-test-matrix (v1.26.0, processor/k8sattributesprocessor)	4m 22s
kubernetes-test-matrix (v1.26.0, receiver/kubeletstatsreceiver)	4m 11s
kubernetes-test-matrix (v1.26.0, receiver/k8sobjectsreceiver)	3m 29s
kubernetes-test-matrix (v1.25.3, receiver/k8sclusterreceiver)	4m 41s
kubernetes-test-matrix (v1.25.3, processor/k8sattributesprocessor)	4m 40s
kubernetes-test-matrix (v1.25.3, receiver/kubeletstatsreceiver)	4m 19s
kubernetes-test-matrix (v1.25.3, receiver/k8sobjectsreceiver)	3m 31s
kubernetes-test-matrix (v1.24.7, receiver/k8sclusterreceiver)	4m 46s
kubernetes-test-matrix (v1.24.7, processor/k8sattributesprocessor)	4m 22s
kubernetes-test-matrix (v1.24.7, receiver/kubeletstatsreceiver)	4m 48s
kubernetes-test-matrix (v1.24.7, receiver/k8sobjectsreceiver)	3m 15s
kubernetes-test-matrix (v1.23.13, receiver/k8sclusterreceiver)	4m 43s
kubernetes-test-matrix (v1.23.13, processor/k8sattributesprocessor)	4m 46s
kubernetes-test-matrix (v1.23.13, receiver/kubeletstatsreceiver)	4m 31s
kubernetes-test-matrix (v1.23.13, receiver/k8sobjectsreceiver)	3m 20s
kubernetes-test	1s
	1h 19m 47s

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