add test private key (#372) #2

Job	Run time
checks / formatting	32s
checks / mypy	46s
checks / ruff	4s
regtest (3.10, 1.5.1, CoreLightningRestWallet) / regtest	3m 3s
regtest (3.10, 1.5.1, LNbitsWallet) / regtest	2m 52s
regtest (3.10, 1.5.1, LndRestWallet) / regtest	2m 41s
tests (ubuntu-latest, 3.10, 1.5.1, false, FakeWallet) / poetry	1m 37s
tests (ubuntu-latest, 3.10, 1.5.1, true, FakeWallet) / poetry	1m 38s
	13m 13s

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