Actually use the correct method for calculating deprecation warning window (#6929)

* Actually use the correct method for calculating deprecation warning windows

* Run formatter

Author: inlined

src/deploy/functions/runtimes/supported.ts

@@ -195,8 +195,8 @@ export function guardVersionSupport(runtime: Runtime, now: Date = new Date()): v
     return;
   }
 
-  const warning = new Date();
-  warning.setDate(deprecation.getDate() - 90);
+  // Subtract 90d (90 * milliseconds per day) to get warning period
+  const warning = new Date(deprecation.getTime() - 90 * 24 * 60 * 60 * 1000);
   if (now >= warning) {
     utils.logLabeledWarning(
       "functions",