Bump itk-elastix from 0.17.1 to 0.19.1 in /envs

Bumps [itk-elastix](https://github.com/InsightSoftwareConsortium/ITKElastix) from 0.17.1 to 0.19.1.
- [Release notes](https://github.com/InsightSoftwareConsortium/ITKElastix/releases)
- [Commits](InsightSoftwareConsortium/ITKElastix@v0.17.1...v0.19.1)

---
updated-dependencies:
- dependency-name: itk-elastix
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

Signed-off-by: dependabot[bot] <support@github.com>

envs/requirements.txt

@@ -16,7 +16,7 @@ importlib-metadata==6.8.0
 importlib-resources==6.1.0
 itk==5.3.0
 itk-core==5.3.0
-itk-elastix==0.17.1
+itk-elastix==0.19.1
 itk-filtering==5.3.0
 itk-io==5.3.0
 itk-numerics==5.3.0