test/utils: fix image creation setup

Between ext2fs 1.46.5 (Ubuntu 22.04) and ext2fs 1.45.5 (Ubuntu 20.04),
there is a breaking change in the default size when creating inode.

> Mke2fs now creates 256 byte inodes by default for
> all non-GNU Hurd file systems.
> (Previously small file systems would be created
using 128 byte inodes.)

Signed-off-by: Mathieu Tortuyaux <mtortuyaux@microsoft.com>

Author: tormath1

src/update_engine/test_utils.cc

@@ -189,7 +189,7 @@ void CreateEmptyExtImageAtPath(const string& path,
   EXPECT_EQ(0, System(StringPrintf("dd if=/dev/zero of=%s"
                                    " seek=%zu bs=1 count=1",
                                    path.c_str(), size)));
-  EXPECT_EQ(0, System(StringPrintf("mkfs.ext2 -b %d -F %s",
+  EXPECT_EQ(0, System(StringPrintf("mkfs.ext2 -b %d -F %s -I 128",
                                    block_size, path.c_str())));
 }