Fix YAML parsing error

[smarter]

I have no idea why this did not explode before merging, but this fixes the following error in the CI:

Exception in thread "main" com.fasterxml.jackson.dataformat.yaml.snakeyaml.error.MarkedYAMLException: while parsing a block collection
 in 'reader', line 7, column 9:
            - title: Implicit Function Types
            ^
expected <block end>, but found BlockMappingStart
 in 'reader', line 23, column 10:
             -title: Multiversal Equality
             ^
 at [Source: java.io.ByteArrayInputStream@7bd3ab02; line: 23, column: 10]
	at com.fasterxml.jackson.dataformat.yaml.snakeyaml.error.MarkedYAMLException.from(MarkedYAMLException.java:27)
	at com.fasterxml.jackson.dataformat.yaml.YAMLParser.nextToken(YAMLParser.java:343)
	at com.fasterxml.jackson.databind.deser.std.UntypedObjectDeserializer.mapArray(UntypedObjectDeserializer.java:179)
	at com.fasterxml.jackson.databind.deser.std.UntypedObjectDeserializer.deserialize(UntypedObjectDeserializer.java:53)
	at com.fasterxml.jackson.databind.deser.std.UntypedObjectDeserializer.mapObject(UntypedObjectDeserializer.java:211)
	at com.fasterxml.jackson.databind.deser.std.UntypedObjectDeserializer.deserialize(UntypedObjectDeserializer.java:51)
	at com.fasterxml.jackson.databind.deser.std.UntypedObjectDeserializer.mapArray(UntypedObjectDeserializer.java:172)
	at com.fasterxml.jackson.databind.deser.std.UntypedObjectDeserializer.deserialize(UntypedObjectDeserializer.java:53)
	at com.fasterxml.jackson.databind.deser.std.MapDeserializer._readAndBindStringMap(MapDeserializer.java:432)
	at com.fasterxml.jackson.databind.deser.std.MapDeserializer.deserialize(MapDeserializer.java:314)
	at com.fasterxml.jackson.databind.deser.std.MapDeserializer.deserialize(MapDeserializer.java:26)
	at com.fasterxml.jackson.databind.ObjectMapper._readMapAndClose(ObjectMapper.java:2888)
	at com.fasterxml.jackson.databind.ObjectMapper.readValue(ObjectMapper.java:2087)
	at dotty.tools.dottydoc.staticsite.Yaml$.apply(Yaml.scala:21)
	at dotty.tools.dottydoc.staticsite.Site$$anonfun$3.apply(Site.scala:90)
	at dotty.tools.dottydoc.staticsite.Site$$anonfun$3.apply(Site.scala:90)
	at scala.Option.map(Option.scala:146)
	at dotty.tools.dottydoc.staticsite.Site.<init>(Site.scala:90)
	at dotty.tools.dottydoc.DocDriver.main(DocDriver.scala:54)
at dotty.tools.dottydoc.Main.main(Main.scala)

[smarter]

@felixmulder It's very weird that this did not fail in #2552, could you investigate?

[smarter]

Merging now to hopefully get the build green.