bindings-java : disable flash attention by default (#3445)

This commit disables flash-attention for the Java binding test so that
the testFullTranscribe test passes.

Without this change the test was failing because the expected output
mismatches after the flash-attention change:
```console
<And so my fellow Americans ask not what your country can do for you ask what you can do for your country.>
but was:
<and so my fellow Americans ask not what your country can do for you ask what you can do for your country>
```

An alternative would also be to update the expected output but it felt
better to keep the same expected output and disable flash-attention and
not just change the expected output to match the new behavior.

bindings/java/src/main/java/io/github/ggerganov/whispercpp/params/WhisperContextParams.java

@@ -20,7 +20,7 @@ public class WhisperContextParams extends Structure {
     /** Use GPU for inference (default = true) */
     public CBool use_gpu;
 
-    /** Use flash attention (default = false) */
+    /** Use flash attention (default = true) */
     public CBool flash_attn;
 
     /** CUDA device to use (default = 0) */