fix: samples/server/petstore/springboot-implicitHeaders/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-COMFASTERXMLJACKSONCORE-3038424
- https://snyk.io/vuln/SNYK-JAVA-ORGSPRINGFRAMEWORK-12008931

Author: snyk-bot

samples/server/petstore/springboot-implicitHeaders/pom.xml

@@ -71,7 +71,7 @@
         <dependency>
             <groupId>org.openapitools</groupId>
             <artifactId>jackson-databind-nullable</artifactId>
-            <version>0.2.6</version>
+            <version>0.2.7</version>
         </dependency>
         <!-- Bean Validation API support -->
         <dependency>