This regression was noticed by Pete Bentley in https://github.com/google/conscrypt/issues/1486

> The [SunX509KeyManager] alias chooser methods now return null when asked for a key of type EC_EC. This feels like an upstream regression introduced in JDK-8359956 because this style of naming (<key type>_<signature type>) is still very much listed in the Java 25 JCA Standard Names document [1] and the change makes no reference to deprecating them.

[1] https://docs.oracle.com/en/java/javase/25/docs/specs/security/standard-names.html#key-types

Pete also noted:

> only affects EC_EC (not other compound signature types) and only affects self signed certificates and probably only affects tests as nothing in the SSLEngine implementation ever uses EC_EC.

Repro:

```
import javax.net.ssl.KeyManager;
import javax.net.ssl.KeyManagerFactory;
import javax.net.ssl.X509KeyManager;
import org.conscrypt.java.security.TestKeyStore;

public final class T {
  public static void main(String[] args) throws Exception {
    TestKeyStore testKeyStore =
        new TestKeyStore.Builder()
            .keyAlgorithms("RSA", "DSA", "EC", "EC_RSA")
            .aliasPrefix("rsa-dsa-ec-dh")
            .build();

    String algorithm = KeyManagerFactory.getDefaultAlgorithm();
    KeyManagerFactory kmf = KeyManagerFactory.getInstance(algorithm);
    kmf.init(testKeyStore.keyStore, testKeyStore.keyPassword);
    for (KeyManager keyManager : kmf.getKeyManagers()) {
      String alias = ((X509KeyManager) keyManager).chooseServerAlias("EC_EC", null, null);
      System.out.println("alias: " + alias);
    }
  }
}
```

openjdk full version "26-ea+9-927"
alias: rsa-dsa-ec-dh-private-ec

openjdk full version "26-ea+10-1053"
alias: null