Add the deprecated field rill_version to rill.yaml validation (#6329

)

* Add the deprecated field `rill_version` to `rill.yaml` validation

* Relax the type

runtime/compilers/rillv1/parse_rillyaml.go

@@ -42,7 +42,10 @@ type VariableDef struct {
 
 // rillYAML is the raw YAML structure of rill.yaml
 type rillYAML struct {
+	// Compiler is the parser version to use. It is not consumed here because at this point a parser has already been chosen.
 	Compiler string `yaml:"compiler"`
+	// RillVersion is deprecated and not used anymore.
+	RillVersion any `yaml:"rill_version"`
 	// Title of the project
 	DisplayName string `yaml:"display_name"`
 	// Title of the project