fix(ctrlx-reporter): Make the $schema field non-nullable

Adjust the docs slightly while at it.

Signed-off-by: Sebastian Schuberth <sebastian@doubleopen.org>

plugins/reporters/ctrlx/src/main/kotlin/CtrlXAutomationModel.kt

@@ -31,10 +31,10 @@ import org.ossreviewtoolkit.utils.spdx.isSpdxExpression
 @Serializable
 internal data class FossInfo(
     /**
-     * The reference to the JSON schema in use.
+     * The reference to the official JSON schema.
      */
     @SerialName("\$schema")
-    val schema: String? = "https://github.com/boschrexroth/json-schema/blob/a84eab6/ctrlx-automation/ctrlx-core/apps/" +
+    val schema: String = "https://github.com/boschrexroth/json-schema/blob/a84eab6/ctrlx-automation/ctrlx-core/apps/" +
         "fossinfo/fossinfo.v1.schema.json",
 
     /**