Add random path when present, don't assert generation header is present

Author: nicktindall

modules/repository-gcs/src/main/java/org/elasticsearch/repositories/gcs/GoogleCloudStorageRetryingInputStream.java

@@ -158,8 +158,6 @@ private Long parseGenerationHeader(HttpResponse response) {
                 assert false : "Unexpected value for x-goog-generation header: " + generationHeader;
                 return null;
             }
-        } else {
-            assert false : "X-Goog-Generation header was missing?";
         }
         return null;
     }

modules/repository-gcs/src/test/java/org/elasticsearch/repositories/gcs/GoogleCloudStorageBlobContainerRetriesTests.java

@@ -605,7 +605,12 @@ public void testContentsChangeWhileStreaming() throws IOException {
             String message = assertThrows(NoSuchFileException.class, () -> readFully(inputStream)).getMessage();
             assertThat(
                 message,
-                startsWith("Blob object [" + key + "] generation [1] unavailable on resume (contents changed, or object deleted):")
+                startsWith(
+                    "Blob object ["
+                        + container.path().buildAsString()
+                        + key
+                        + "] generation [1] unavailable on resume (contents changed, or object deleted):"
+                )
             );
         }
     }