Bump flatten-json from 0.1.13 to 0.1.14 in /stix_shifter (#1613)

Bumps [flatten-json](https://github.com/amirziai/flatten) from 0.1.13 to 0.1.14.
- [Release notes](https://github.com/amirziai/flatten/releases)
- [Commits](https://github.com/amirziai/flatten/commits)

---
updated-dependencies:
- dependency-name: flatten-json
  dependency-type: direct:production
  update-type: version-update:semver-patch
...

Signed-off-by: dependabot[bot] <[email protected]>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

stix_shifter/requirements.txt

@@ -8,7 +8,7 @@ attrs==23.1.0
 azure-identity==1.15.0
 colorlog==6.7.0
 flask==3.0.0
-flatten_json==0.1.13
+flatten_json==0.1.14
 json-fix==0.5.2
 jsonmerge==1.9.2
 pyOpenSSL==23.3.0