[Kotlin] Fix default value for kotlin class (!10407) · Merge requests · OpenAPI Tools / openapi-generator

Created by: Fs02

Fix possible typo on kotlin defaultValue in mustache template which cause default value not generated
Validated on different project by overriding data_class_opt_var.mustache

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Pull Request title clearly describes the work in the pull request and Pull Request description provides details about how to validate the work. Missing information here may result in delayed response from the community.
Run the following to build the project and update samples:
```
./mvnw clean package 
./bin/generate-samples.sh
./bin/utils/export_docs_generators.sh
```
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cc: @jimschubert @dr4ke616 @karismann @Zomzog @andrewemery @4brunu @yutaka0m