revert underscore as a multiversion separator

Emby.Naming/Video/VideoListResolver.cs

@@ -235,7 +235,6 @@ namespace Emby.Naming.Video
                 // The CleanStringParser should have removed common keywords etc.
                 return string.IsNullOrEmpty(testFilename)
                        || testFilename[0] == '-'
-                       || testFilename[0] == '_'
                        || Regex.IsMatch(testFilename, @"^\[([^]]*)\]");
             }
 

tests/Jellyfin.Naming.Tests/Video/MultiVersionTests.cs

@@ -295,12 +295,9 @@ namespace Jellyfin.Naming.Tests.Video
                 FullName = i
             }).ToList()).ToList();
 
-            Assert.Single(result);
+            Assert.Equal(7, result.Count);
             Assert.Empty(result[0].Extras);
-            Assert.Equal(6, result[0].AlternateVersions.Count);
-            Assert.False(result[0].AlternateVersions[2].Is3D);
-            Assert.True(result[0].AlternateVersions[3].Is3D);
-            Assert.True(result[0].AlternateVersions[4].Is3D);
+            Assert.Empty(result[0].AlternateVersions);
         }
 
         [Fact]