Leak in SystemJobService

Hi everyone,

we're using WorkManager in an app in which we've also [LeakCanary](https://square.github.io/leakcanary/) configured and we always receive this warning after a run of each Periodic Worker:

```
16:49:08.888 LeakCanary ​
====================================
HEAP ANALYSIS RESULT
====================================
1 APPLICATION LEAKS

References underlined with "~~~" are likely causes.
Learn more at https://squ.re/leaks.

774 bytes retained by leaking objects
Signature: 6491376cfe66b1cac0d47b3ae180fd902719aa5
┬───
│ GC Root: Global variable in native code
│
├─ android.app.job.JobService$1 instance
│ Leaking: UNKNOWN
│ Retaining 802 B in 15 objects
│ Anonymous subclass of android.app.job.IJobService$Stub
│ this$0 instance of androidx.work.impl.background.systemjob.SystemJobService
│ ↓ JobService$1.this$0
│ ~~~~~~
╰→ androidx.work.impl.background.systemjob.SystemJobService instance
​ Leaking: YES (ObjectWatcher was watching this because androidx.work.impl.background.systemjob.SystemJobService
​ received Service#onDestroy() callback)
​ Retaining 774 B in 14 objects
​ key = 155d4c85-1073-4df1-bd0f-250b40c959c8
​ watchDurationMillis = 5248
​ retainedDurationMillis = 246
​ mApplication instance of xx.yy.MyApp
​ mBase instance of android.app.ContextImpl
====================================
0 LIBRARY LEAKS

A Library Leak is a leak caused by a known bug in 3rd party code that you do not have control over.
See https://square.github.io/leakcanary/fundamentals-how-leakcanary-works/#4-categorizing-leaks
====================================
0 UNREACHABLE OBJECTS

An unreachable object is still in memory but LeakCanary could not find a strong reference path
from GC roots.
====================================
METADATA

Please include this in bug reports and Stack Overflow questions.

Build.VERSION.SDK_INT: 23
Build.MANUFACTURER: alps
LeakCanary version: 2.6
App process name: xx.yy.MyApp
Stats: LruCache[maxSize=3000,hits=101,misses=300675,hitRate=0%]
RandomAccess[bytes=11383030,reads=300675,travel=696095628841,range=23369842,size=28770980]
Heap dump reason: 1 retained objects, app is not visible
Analysis duration: 202141 ms
Heap dump file path: /storage/emulated/0/Download/leakcanary-xx.yy.MyApp/2021-03-08_16-45-32_740.
hprof
Heap dump timestamp: 1615218548838
Heap dump duration: 13889 ms
====================================
```

WorkManager library in use: `androidx.work:work-rxjava2:2.5.0`
LeakCanary library in use: `com.squareup.leakcanary:leakcanary-android:2.6`

Any advice? Did you see this warning yet?

I don't know if can be a useful info, but the app we're developing is a system app used on embedded device (Android based, obviously)

Bắt đầu với LeakCanary trace của issue và vòng đời của SystemJobService trên Android API 23, sau đó tái hiện bằng WorkManager 2.5.0 và LeakCanary 2.6 với một periodic worker. Hoàn thành nghĩa là xác định liệu service bị giữ lại có phải là một library leak có thể tái hiện hay không, đồng thời ghi lại hoặc sửa kết quả; issue không nêu tên file nguồn hay test nào.

Do mô hình lập chỉ mục viết ra từ nội dung của issue.