fix: use hardcoded test credentials instead of System.getenv

The test was using System.getenv() to read API credentials, but in the
Gradle test JVM credentials are injected as system properties from
local.properties, causing a NullPointerException in buildJWT().

Made-with: Cursor

Author: itsmeadi

src/test/java/io/getstream/StreamHTTPClientTest.java

@@ -151,7 +151,9 @@ void testCustomOkHttpClientPreservesConfig() {
 
     var sdkClient =
         new StreamSDKClient(
-            System.getenv("STREAM_API_KEY"), System.getenv("STREAM_API_SECRET"), customHttp);
+            "d2sj6pudbhz7",
+            "qs9ukpbmau9s4kgz5bndfrhse9wc4v54w5u2zzawgt4fmjx42zkwegsxnsr32r9x",
+            customHttp);
     OkHttpClient builtClient = sdkClient.getHttpClient().getHttpClient();
 
     assertSame(customPool, builtClient.connectionPool());