Missing timezone string for utc+5:30 TZ

Date format missing timezone string

## Issue Description
```
flight_schedule_date = arrow.now("America/New_York")
flight_landing_date = flight_schedule_date.shift(hours=28).to('+05:30')

print(f'flight scheduled departure is {flight_schedule_date.format("DD,MMM HH:mm A ZZZ")} and expected arrival at destination is {flight_landing_date.format("DD,MMM HH:mm A ZZZ")}')
```
**Output**
flight scheduled departure is 22,May 10:40 AM EDT and expected arrival at destination is 24,May 00:10 AM
**which is missing "IST" at end**

But when I add ZZ, I get correct tz expression
flight scheduled departure is 22,May 10:39 AM **EDT** and expected arrival at destination is 24,May 00:09 AM **+05:30**

## System Info

- 🖥 **OS name and version**: macOS 10.15.7
- 🐍 **Python version**: 3.8.2
- 🏹 **Arrow version**: 1.2.2

Start by reproducing the issue's Arrow 1.2.2 example and compare the ZZZ and ZZ outputs for the +05:30 timezone. Trace the timezone-name formatting path used by format(), then verify the chosen behavior with a focused regression test showing what should appear for this offset.

Written by the indexing model from the issue text.