Here's the test code:

```java
DateTimeFormatter shortFormat =
    new DateTimeFormatterBuilder()
        .appendPattern("GG")
        .toFormatter(Locale.ROOT);
DateTimeFormatter longFormat =
    new DateTimeFormatterBuilder()
        .appendPattern("GGGG")
        .toFormatter(Locale.ROOT);
System.out.println("short era: " + shortFormat.format(IsoEra.BCE));
System.out.println(" long era: " + longFormat.format(IsoEra.BCE));
```

Java 21 (the result is the same for all Java versions below 21):
short era: BC
 long era: BCE

Java 22.ea.25-open:
short era: BCE
 long era: BCE

The issue was discovered as I added Java 22 to the CI matrix in pgjdbc: https://github.com/pgjdbc/pgjdbc/pull/3026