`_parse_additional_json` ignore `FW.json(.gz)`

[janosh]

Ignore FW.json(.gz) so jobflow doesn't try to parse prev_vasp_dir OutputReferences from it.

Reason This was causing atomate2 MP workflows (see https://github.com/materialsproject/atomate2/pull/504) to fail with

ValueError: Could not resolve reference 7f5a7f14-464c-4a5b-85f9-8d11b595be3b not in store or cache

if a FW.json.gz was present in the job's output directory.

[codecov-commenter]

Codecov Report

All modified lines are covered by tests :white_check_mark:

Comparison is base (8184d2d) 91.34% compared to head (9c41d8e) 89.66%.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #864 +/- ## ========================================== - Coverage 91.34% 89.66% -1.68% ========================================== Files 138 108 -30 Lines 12749 9603 -3146 ========================================== - Hits 11646 8611 -3035 + Misses 1103 992 -111 ``` | [Files](https://app.codecov.io/gh/materialsproject/emmet/pull/864?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=materialsproject) | Coverage Δ | | |---|---|---| | [emmet-core/emmet/core/tasks.py](https://app.codecov.io/gh/materialsproject/emmet/pull/864?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=materialsproject#diff-ZW1tZXQtY29yZS9lbW1ldC9jb3JlL3Rhc2tzLnB5) | `87.23% <100.00%> (ø)` | | ... and [47 files with indirect coverage changes](https://app.codecov.io/gh/materialsproject/emmet/pull/864/indirect-changes?src=pr&el=tree-more&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=materialsproject)

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