PpgPublicKeyParser: Warn about uncertified subkeys

The Tor and the Electrum developer's subkeys are signed by their master
keys. The PpgPublicKeyParser enforces this behavior. Unfortunately,
this is not true for all Bitcoin Core developers. One example where this
happens is when we try to verify the key with the fingerprint
`0x57FF9BDBCC301009`.

build-logic/gradle-tasks/src/main/kotlin/bisq/gradle/tasks/signature/PpgPublicKeyParser.kt

@@ -1,5 +1,6 @@
 package bisq.gradle.tasks.signature
 
+import org.bouncycastle.openpgp.PGPException
 import org.bouncycastle.openpgp.PGPPublicKey
 import org.bouncycastle.openpgp.PGPPublicKeyRing
 import org.bouncycastle.openpgp.PGPUtil
@@ -9,6 +10,7 @@ import org.bouncycastle.util.encoders.Hex
 import org.gradle.api.GradleException
 import java.io.ByteArrayInputStream
 import java.net.URL
+import java.security.InvalidKeyException
 
 class PpgPublicKeyParser(
     private val primaryKeyFingerprint: String,
@@ -76,14 +78,21 @@ class PpgPublicKeyParser(
         subKeys.forEach { subKey ->
             var hasValidSignature = false
             subKey.keySignatures.forEach { signature ->
-                signature.init(
-                    JcaPGPContentVerifierBuilderProvider().setProvider("BC"),
-                    masterKey!!
-                )
-                val isSubKeySignedByMasterKey = signature.verifyCertification(masterKey!!, subKey)
+                try {
+                    signature.init(
+                        JcaPGPContentVerifierBuilderProvider().setProvider("BC"),
+                        masterKey!!
+                    )
+                    val isSubKeySignedByMasterKey = signature.verifyCertification(masterKey!!, subKey)
 
-                if (isSubKeySignedByMasterKey) {
-                    hasValidSignature = true
+                    if (isSubKeySignedByMasterKey) {
+                        hasValidSignature = true
+                    }
+                } catch (e: PGPException) {
+                    if (e.underlyingException is InvalidKeyException) {
+                        println("Warning: Can't verify subkey `${subKey.keyID}` with masterkey `${masterKey!!.keyID}`.")
+                        hasValidSignature = true
+                    }
                 }
             }