Build: Bump datamodel-code-generator from 0.26.3 to 0.26.4

Bumps [datamodel-code-generator](https://github.com/koxudaxi/datamodel-code-generator) from 0.26.3 to 0.26.4.
- [Release notes](https://github.com/koxudaxi/datamodel-code-generator/releases)
- [Commits](koxudaxi/datamodel-code-generator@0.26.3...0.26.4)

---
updated-dependencies:
- dependency-name: datamodel-code-generator
  dependency-type: direct:production
  update-type: version-update:semver-patch
...

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

open-api/requirements.txt

@@ -16,4 +16,4 @@
 # under the License.
 
 openapi-spec-validator==0.7.1
-datamodel-code-generator==0.26.3
+datamodel-code-generator==0.26.4