category with no apps should be ignored, even if defined in config

https://gitlab.com/fdroid/fdroidclient/-/issues/2619#note_1421280589

The test needed to change because the test index files contained category
definitions that were not ever used in the "copy tests/repo, generate java/gpg
keys, update, and gpgsign" test in tests/run-tests.

tests/repo/entry.json

@@ -3,7 +3,7 @@
   "version": 20002,
   "index": {
     "name": "/index-v2.json",
-    "sha256": "b613858aa7a2ec476fcef5c841a5b8ff4b3b0f67f07678da981e2843f49c71ba",
+    "sha256": "5e3c0eaafd99d3518da2bb2bc7565b2ebcb17775a2f4ccc33b7336901ec71a6f",
     "size": 53283,
     "numPackages": 10
   },

tests/repo/index-v1.json

@@ -174,6 +174,8 @@
         "NonFreeNet"
       ],
       "categories": [
+        "Multimedia",
+        "Security",
         "Time"
       ],
       "suggestedVersionName": "1.5",

tests/repo/index-v2.json

@@ -553,6 +553,8 @@
       "metadata": {
         "added": 1498176000000,
         "categories": [
+          "Multimedia",
+          "Security",
           "Time"
         ],
         "issueTracker": "https://github.com/miguelvps/PoliteDroid/issues",

tests/repo/index.xml

@@ -311,8 +311,8 @@ APK is called F-Droid Privileged Extension.</desc>
 		<icon>com.politedroid.6.png</icon>
 		<desc>Activates silent mode during calendar events.</desc>
 		<license>GPL-3.0-only</license>
-		<categories>Time</categories>
-		<category>Time</category>
+		<categories>Multimedia,Security,Time</categories>
+		<category>Multimedia</category>
 		<web></web>
 		<source>https://github.com/miguelvps/PoliteDroid</source>
 		<tracker>https://github.com/miguelvps/PoliteDroid/issues</tracker>