[BLD] Make Slack notifications consistent (#5238)

## Description of changes

I noticed that our Slack notifications for workflow failures are
slightly inconsistent. This makes them all have the same payload
structure which is:
```
Title (aka what failed)
Workflow: <name of the workflow>
Run: <link to run>
Ref: <link to ref>
Author: <if possible>
[Args like "Plane"]: 
...
```

## Test plan

This only changes the payload for the existing functionality, so is
pretty safe.