### Briefly, what does this PR introduce?
This fixes the dead links to the tgeo (brycecanyon.root ->
epic_brycecanyon.root) and constants toml/out (epic_brycecanyon.out ->
epic_brycecanyon_constants.out).

The latter could have been caught by a link checker after the website
deploy, but the first is working but simply doesn't load the correct
geometry file (or any geometry file at all).

### What kind of change does this PR introduce?
- [x] Bug fix (issue: dead links)
- [ ] New feature (issue #__)
- [ ] Documentation update
- [ ] Other: __

### Please check if this PR fulfills the following:
- [ ] Tests for the changes have been added
- [ ] Documentation has been added / updated
- [ ] Changes have been communicated to collaborators

### Does this PR introduce breaking changes? What changes might users
need to make to their code?
No.

### Does this PR change default behavior?
No.