fix: update bot token secret name (#5424)
There seem to be some confusion around the github bot tokens used in
this repository. This PR aligns the naming of the remaining token to be
very specific and clear.
This token is a fine grained access token living in the `prismabots`
account and granting access to github actions of the
`prisma/engines-wrapper` repo
Once that token has been approved by Github Admins and this PR is merged
we can delete the following two secrets from github actions for this
repo as they seem unused:
- `BOT_TOKEN_PRISMA_ENGINES_BUILD`
- `PRISMA_BOT_TOKEN`
