GitHub Action CI: Add Go source file format check (#6090)

https://github.com/XTLS/Xray-core/pull/6057#issuecomment-4364819830

And https://github.com/XTLS/Xray-core/pull/6149#issuecomment-4546876261

proxy/vless/encryption/client.go

@@ -79,7 +79,7 @@ func (i *ClientInstance) Handshake(conn net.Conn) (*CommonConn, error) {
 	var nfsKey []byte
 	var lastCTR cipher.Stream
 	for j, k := range i.NfsPKeys {
-		var index = 32
+		index := 32
 		if k, ok := k.(*ecdh.PublicKey); ok {
 			privateKey, _ := ecdh.X25519().GenerateKey(rand.Reader)
 			copy(relays, privateKey.PublicKey().Bytes())

proxy/vless/encryption/server.go

@@ -135,7 +135,7 @@ func (i *ServerInstance) Handshake(conn net.Conn, fallback *[]byte) (*CommonConn
 		if lastCTR != nil {
 			lastCTR.XORKeyStream(relays, relays[:32]) // recover this relay
 		}
-		var index = 32
+		index := 32
 		if _, ok := k.(*mlkem.DecapsulationKey768); ok {
 			index = 1088
 		}