docs: Update typo simnet to signet #154

Job	Run time
go_sec_covenant_signer	1m 18s
docker_pipeline_covenant_signer / prepare-metadata	1s
docker_pipeline_covenant_signer / dockerfile_lint	22s
lint_test / build	3m 9s
lint_test / integration-tests	7m 42s
lint_test / lint	3m 13s
lint_test / unit-tests	3m 8s
docker_pipeline / dockerfile_lint	22s
docker_pipeline / prepare-metadata	1s
lint_test / check-mock-gen	0s
lint_test / gosec	2m 34s
docker_pipeline_covenant_signer / docker_build (linux/amd64, ubuntu-24.04)	1m 32s
docker_pipeline_covenant_signer / docker_build (linux/arm64, ubuntu-24.04-arm64)	1m 37s
docker_pipeline / docker_build (linux/amd64, ubuntu-24.04)	2m 52s
docker_pipeline / docker_build (linux/arm64, ubuntu-24.04-arm64)	2m 49s
docker_pipeline_covenant_signer / merge_dockerhub	0s
docker_pipeline_covenant_signer / merge_ecr	0s
docker_pipeline_covenant_signer / vulnerability_scan	0s
docker_pipeline / merge_dockerhub	0s
docker_pipeline / merge_ecr	0s
docker_pipeline / vulnerability_scan	0s
	30m 40s

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