Fix build with libheif 1.21
https://github.com/AcademySoftwareFoundation/OpenImageIO/pull/4851

Index: src/heif.imageio/heifinput.cpp
--- src/heif.imageio/heifinput.cpp.orig
+++ src/heif.imageio/heifinput.cpp
@@ -390,8 +390,13 @@ HeifInput::read_native_scanline(int subimage, int mipl
 #else
     int ystride = 0;
 #endif
+#if LIBHEIF_NUMERIC_VERSION >= MAKE_LIBHEIF_VERSION(1, 20, 2, 0)
+    const uint8_t* hdata = m_himage.get_plane2(heif_channel_interleaved,
+                                               &ystride);
+#else
     const uint8_t* hdata = m_himage.get_plane(heif_channel_interleaved,
                                               &ystride);
+#endif
     if (!hdata) {
         errorfmt("Unknown read error");
         return false;
