Fix AwsStsHttpHandlerTests

Author: DaveCTurner

test/fixtures/aws-sts-fixture/src/test/java/fixture/aws/sts/AwsStsHttpHandlerTests.java

@@ -134,7 +134,7 @@ private record TestHttpResponse(RestStatus status, BytesReference body) {}
     private static TestHttpResponse handleRequest(AwsStsHttpHandler handler, Map<String, String> body) {
         final var httpExchange = new TestHttpExchange(
             "POST",
-            "/assume-role-with-web-identity/",
+            "/",
             new BytesArray(
                 body.entrySet()
                     .stream()