chore: Update c2pa-rs to v 0.78.4 (#241)

* Update c2pa-native-version.txt

* Update test_unit_tests.py

Author: tmathern

c2pa-native-version.txt

@@ -1 +1 @@
-c2pa-v0.78.3
+c2pa-v0.78.4

tests/test_unit_tests.py

@@ -70,7 +70,7 @@ def load_test_settings_json():
 class TestC2paSdk(unittest.TestCase):
     def test_sdk_version(self):
         # This test verifies the native libraries used match the expected version.
-        self.assertIn("0.78.3", sdk_version())
+        self.assertIn("0.78.4", sdk_version())
 
 
 class TestReader(unittest.TestCase):