add `to_omni_account` fn unit tests #8910

Job	Run time
set-condition	9s
fmt	1m 22s
sequentialise	2s
tee-check	24m 50s
parachain-build-dev	52m 4s
parachain-clippy	16m 23s
bitacross-build	32m 50s
identity-build	19m 19s
omni-executor-build	2m 44s
omni-executor-check	0s
parachain-runtime-test	24m 3s
parachain-unit-test	8m 8s
lit-sign-bitcoin	10m 27s
litentry	23m 7s
lit-di-identity-test	20m 8s
paseo	23m 13s
lit-dr-vc-test	9m 26s
${{ matrix.test_name }}	0s
lit-parentchain-nonce	7m 28s
omni-test	1m 18s
lit-test-failed-parentchain-extrinsic	9m 2s
lit-omni-account-test	12m 24s
lit-native-request-vc-test	11m 51s
push-docker	0s
	5h 10m 18s

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