tests/java_api/general: Correct the graal_c_api run

Due to an incomplete update after a testcase copy-paste, this Java test
runs agains the JNI bindings whereas it is supposed to run with the
Native-Image ones. Fix the test to run with the correct bindings.

Author: HugoGGuerrier

testsuite/tests/java_api/general/graal_c_api/test.py

@@ -12,7 +12,7 @@
 
 build_and_run(
     lkt_file="expected_concrete_syntax.lkt",
-    java_main="BindingsTests",
+    ni_main="BindingsTests",
     default_unit_provider=LibraryEntity(
         "Libfoolang.Helpers", "Create_Unit_Provider",
     ),