gitleaks: Ignore mock SSH keys

Quiesce Red Hat's security scanner about allegedly leaking private SSH
keys. These are static keys for our unit tests.

Author: martinpitt

.gitleaks.toml

@@ -0,0 +1,5 @@
+# # help Red Hat ignore false positives during its code scans
+[allowlist]
+paths = [
+    'src/ssh/mock.*key',
+]