fix: samples/meta-codegen/lib/pom.xml to reduce vulnerabilities

The following vulnerabilities are fixed with an upgrade:
- https://snyk.io/vuln/SNYK-JAVA-COMFASTERXMLJACKSONCORE-3038426
- https://snyk.io/vuln/SNYK-JAVA-ORGMOZILLA-1314295
- https://snyk.io/vuln/SNYK-JAVA-COMFASTERXMLJACKSONCORE-2421244
- https://snyk.io/vuln/SNYK-JAVA-COMFASTERXMLJACKSONCORE-3038424
- https://snyk.io/vuln/SNYK-JAVA-COMMONSIO-8161190
- https://snyk.io/vuln/SNYK-JAVA-COMGOOGLEGUAVA-5710356
- https://snyk.io/vuln/SNYK-JAVA-COMFASTERXMLJACKSONCORE-2326698
- https://snyk.io/vuln/SNYK-JAVA-COMGOOGLEGUAVA-1015415
- https://snyk.io/vuln/SNYK-JAVA-COMMONSCODEC-561518

samples/meta-codegen/lib/pom.xml

@@ -121,7 +121,7 @@
     </dependencies>
     <properties>
         <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
-        <openapi-generator-version>5.2.1-SNAPSHOT</openapi-generator-version>
+        <openapi-generator-version>7.6.0</openapi-generator-version>
         <maven-plugin-version>1.0.0</maven-plugin-version>
         <junit-version>4.8.1</junit-version>
     </properties>