`--version` outputs shows `built` as `-999999999-01-01T00:00:00+18:00`

Bug Report Checklist

• Have you provided a full/minimal spec to reproduce the issue?
• Have you validated the input using an OpenAPI validator (example)?
• Have you tested with the latest master to confirm the issue still exists?
• Have you searched for related issues/PRs?
• What's the actual output vs expected output?
• [Optional] Sponsorship to speed up the bug fix or feature request (example)

Description

When you check the built time via the --version flag, you'll see it returns a nonsense date.

❯ openapi-generator --version
openapi-generator-cli 7.1.0
  commit : e2a62ac
  built  : -999999999-01-01T00:00:00+18:00
  source : https://github.com/openapitools/openapi-generator
  docs   : https://openapi-generator.tech/

openapi-generator version

The most recent one (7.1.0), the latest master, and probably all versions?

Steps to reproduce

openapi-generator --version

Suggest a fix

The git plugin should include the build time too.

--- a/modules/openapi-generator/pom.xml
+++ b/modules/openapi-generator/pom.xml
@@ -60,7 +60,7 @@
                     <generateGitPropertiesFilename>${project.build.outputDirectory}/openapi-generator-git.properties</generateGitPropertiesFilename>
                     <!-- REVIEWER NOTE: Never allow external contributors to change these without full clarification. -->
                     <includeOnlyProperties>
-                        <includeOnlyProperty>^git.build.version$</includeOnlyProperty>
+                        <includeOnlyProperty>^git.build.(time|version)$</includeOnlyProperty>
                         <includeOnlyProperty>^git.commit.id.(abbrev|full)$</includeOnlyProperty>
                     </includeOnlyProperties>
                     <commitIdGenerationMode>full</commitIdGenerationMode>

Start in modules/openapi-generator/pom.xml, where the git plugin's includeOnlyProperty entries omit the build time. Run openapi-generator --version before and after the change. Done means the built field reports an actual build timestamp instead of -999999999-01-01T00:00:00+18:00.