asset/btc: fix format time for assetdb-backup/btc filepath (decred#3056)

changed:
	  assetdb-backup/btc/regtest/2024-11-03T16:59:15
	to:
	  assetdb-backup/btc/regtest/2024-11-03T17_24_29

	`:` invalid for Windows filepath

Co-authored-by: dev-warrior777 <>

client/asset/btc/spv_wrapper.go

@@ -955,7 +955,7 @@ func (w *spvWallet) connect(ctx context.Context, wg *sync.WaitGroup) (err error)
 // moveWalletData will move all wallet files to a backup directory, but leaving
 // the logs folder.
 func (w *spvWallet) moveWalletData(backupDir string) error {
-	timeString := time.Now().Format("2006-01-02T15:04:05")
+	timeString := time.Now().Format("2006-01-02T15_04_05")
 	backupFolder := filepath.Join(backupDir, w.chainParams.Name, timeString)
 	err := os.MkdirAll(backupFolder, 0744)
 	if err != nil {