Codechange: Declare all IntervalTimers const, which can be const.

src/company_cmd.cpp

@@ -812,7 +812,7 @@ void OnTick_Companies()
  * A year has passed, update the economic data of all companies, and perhaps show the
  * financial overview window of the local company.
  */
-static IntervalTimer<TimerGameEconomy> _economy_companies_yearly({TimerGameEconomy::YEAR, TimerGameEconomy::Priority::COMPANY}, [](auto)
+static const IntervalTimer<TimerGameEconomy> _economy_companies_yearly({TimerGameEconomy::YEAR, TimerGameEconomy::Priority::COMPANY}, [](auto)
 {
 	/* Copy statistics */
 	for (Company *c : Company::Iterate()) {