Bump test/fixtures/prism from e6d7144 to b12fe69

Bumps [test/fixtures/prism](https://github.com/ruby/prism) from `e6d7144` to `b12fe69`.
- [Release notes](https://github.com/ruby/prism/releases)
- [Commits](ruby/prism@e6d7144...b12fe69)

---
updated-dependencies:
- dependency-name: test/fixtures/prism
  dependency-version: b12fe69200bc142a9a7dc054a3e16a1571291559
  dependency-type: direct:production
...

Signed-off-by: dependabot[bot] <[email protected]>

Author: dependabot[bot]