Fix skin parser not stripping whitespace before parsing

osu.Game.Tests/Resources/skin-with-space.ini

@@ -0,0 +1,2 @@
+[General] 
+Version: 2

osu.Game.Tests/Skins/LegacySkinDecoderTest.cs

@@ -91,6 +91,15 @@ public void TestDecodeSpecifiedVersion()
                 Assert.AreEqual(2.0m, decoder.Decode(stream).LegacyVersion);
         }
 
+        [Test]
+        public void TestStripWhitespace()
+        {
+            var decoder = new LegacySkinDecoder();
+            using (var resStream = TestResources.OpenResource("skin-with-space.ini"))
+            using (var stream = new LineBufferedReader(resStream))
+                Assert.AreEqual(2.0m, decoder.Decode(stream).LegacyVersion);
+        }
+
         [Test]
         public void TestDecodeLatestVersion()
         {

osu.Game/Beatmaps/Formats/LegacyDecoder.cs

@@ -36,6 +36,8 @@ protected override void ParseStreamInto(LineBufferedReader stream, T output)
                 if (ShouldSkipLine(line))
                     continue;
 
+                line = line.Trim();
+
                 if (line.StartsWith('[') && line.EndsWith(']'))
                 {
                     if (!Enum.TryParse(line[1..^1], out section))