Upgrade org.openapi.generator 7.7.0

[qmonmert]

Fix #26615

Related to OpenAPITools/openapi-generator#18753

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[mshima]

We have removed buildscript block from gradle config, if possible we should avoid re-adding.
If necessary the build script should be optional on enableSwaggerCodegen.

[mshima]

Not needed anymore.
Gradle seems to use different dependency resolution with convention plugins.
The issue does not happen with convention plugins.
Thanks @qmonmert.