Consistently name argument, unbreak Android OSS build

Summary:
57eb56f broke Android OSS due to a variable rename that I missed in a rebase.

Eg:
https://github.com/facebook/react-native/actions/runs/26894263379/job/79328683517

```
e: warnings found and -Werror specified
w: file:///__w/react-native/react-native/packages/react-native/ReactAndroid/src/test/java/com/facebook/react/devsupport/MultipartStreamReaderTest.kt:203:15 The corresponding parameter in the supertype 'CallCountTrackingChunkCallback' is named 'isLastChunk'. This may cause problems when calling this function with named arguments.

> Task :packages:react-native:ReactAndroid:compileDebugOptimizedUnitTestKotlin

> Task :packages:react-native:ReactAndroid:compileDebugOptimizedUnitTestKotlin FAILED
> Task :react-native_popup-menu-android:extractReleaseAnnotations
e: warnings found and -Werror specified
```

Changelog: Internal

Differential Revision: D107397221

Author: robhogan

packages/react-native/ReactAndroid/src/test/java/com/facebook/react/devsupport/MultipartStreamReaderTest.kt

@@ -200,9 +200,9 @@ class MultipartStreamReaderTest {
           override fun onChunkComplete(
               headers: Map<String, String>,
               body: BufferedSource,
-              done: Boolean,
+              isLastChunk: Boolean,
           ) {
-            super.onChunkComplete(headers, body, done)
+            super.onChunkComplete(headers, body, isLastChunk)
 
             // Lookup using canonical case should still work.
             assertThat(headers["Content-Type"]).isEqualTo("application/json")