test: align by-handle Content-Disposition expectations with the vanilla ASCII fallback

The fallback transliterates (NFD + strip combining marks + drop non-ASCII),
it does not substitute underscores. Two expectations in this file still
assumed the old underscore output.

Author: milanmajchrak

dspace-server-webapp/src/test/java/org/dspace/app/rest/BitstreamByHandleRestControllerIT.java

@@ -512,8 +512,8 @@ public void downloadBitstreamByHandleCjkFilename() throws Exception {
                         + "/%E6%97%A5%E6%9C%AC%E8%AA%9E.txt")))
                 .andExpect(status().isOk())
                 .andExpect(header().string(HttpHeaders.CONTENT_DISPOSITION,
-                        // CJK chars replaced with _ in ASCII fallback; filename* has UTF-8 encoding
-                        equalTo("attachment; filename=\"___.txt\"; "
+                        // CJK has no ASCII decomposition, so it drops out of the fallback entirely
+                        equalTo("attachment; filename=\".txt\"; "
                                 + "filename*=UTF-8''%E6%97%A5%E6%9C%AC%E8%AA%9E.txt")))
                 .andExpect(content().string(bitstreamContent));
     }
@@ -592,7 +592,7 @@ public void downloadBitstreamByHandleComplexFilename() throws Exception {
                         + "/M%C3%A9di%C3%A1%20(%2B)%239)%20ano")))
                 .andExpect(status().isOk())
                 .andExpect(header().string(HttpHeaders.CONTENT_DISPOSITION,
-                        equalTo("attachment; filename=\"M_di_ (+)#9) ano\"; "
+                        equalTo("attachment; filename=\"Media (+)#9) ano\"; "
                                 + "filename*=UTF-8''M%C3%A9di%C3%A1%20%28%2B%29%239%29%20ano")))
                 .andExpect(content().string(bitstreamContent));
     }