Contracts Bump ApiVersion and add test (#3619)

ApiVersion should have been bumped with
https://github.com/paritytech/polkadot-sdk/pull/3606
this does that and add a test so we don't forget to do that everytime

substrate/frame/contracts/proc-macro/src/lib.rs

@@ -497,9 +497,14 @@ fn expand_docs(def: &EnvDef) -> TokenStream2 {
 fn expand_env(def: &EnvDef, docs: bool) -> TokenStream2 {
 	let impls = expand_impls(def);
 	let docs = docs.then_some(expand_docs(def)).unwrap_or(TokenStream2::new());
+	let stable_api_count = def.host_funcs.iter().filter(|f| f.is_stable).count();
 
 	quote! {
 		pub struct Env;
+
+		#[cfg(test)]
+		pub const STABLE_API_COUNT: usize = #stable_api_count;
+
 		#impls
 		/// Documentation of the API (host functions) available to contracts.
 		///