Fix offset formatting in ISO strings for format=basic (#1660)

Author: snowwwz

src/datetime.js

@@ -280,12 +280,16 @@ function toISOTime(
     } else if (o.o < 0) {
       c += "-";
       c += padStart(Math.trunc(-o.o / 60));
-      c += ":";
+      if (extended) {
+        c += ":";
+      }
       c += padStart(Math.trunc(-o.o % 60));
     } else {
       c += "+";
       c += padStart(Math.trunc(o.o / 60));
-      c += ":";
+      if (extended) {
+        c += ":";
+      }
       c += padStart(Math.trunc(o.o % 60));
     }
   }

test/datetime/format.test.js

@@ -280,6 +280,7 @@ test("DateTime#toISOTime() can omit the offset", () => {
 
 test("DateTime#toISOTime() can output the basic format", () => {
   expect(dt.toISOTime({ format: "basic" })).toBe("092354.123Z");
+  expect(dt.setZone("America/New_York").toISOTime({ format: "basic" })).toBe("052354.123-0400");
   const dt2 = dt.set({ second: 0, millisecond: 0 });
   expect(dt2.toISOTime({ format: "basic", suppressMilliseconds: true })).toBe("092300Z");
   expect(dt2.toISOTime({ format: "basic", suppressSeconds: true })).toBe("0923Z");