Use jni_libs instead of required for signapk conscrypt JNI

Using jni_libs tells Soong to install the JNI library into
a genrule sandbox alongside the java binary.

Bug: 124313442
Test: m checkbuild
Change-Id: Ia550102c7aa483497f95ac2ea8bb01bce89ae9c1

tools/signapk/Android.bp

@@ -27,7 +27,7 @@ java_binary_host {
         "conscrypt-unbundled",
     ],
 
-    required: ["libconscrypt_openjdk_jni"],
+    jni_libs: ["libconscrypt_openjdk_jni"],
 
     // The post-build signing tools need signapk.jar (and its shared libraries,
     // handled in their own Android.bp files)