Bump mavenVersion from 3.6.3 to 3.9.9 (#283)

* Bump mavenVersion from 3.6.3 to 3.9.9

Bumps `mavenVersion` from 3.6.3 to 3.9.9.

Updates `org.apache.maven:maven-plugin-api` from 3.6.3 to 3.9.9
- [Release notes](https://github.com/apache/maven/releases)
- [Commits](apache/maven@maven-3.6.3...maven-3.9.9)

Updates `org.apache.maven:maven-artifact` from 3.6.3 to 3.9.9

Updates `org.apache.maven:maven-core` from 3.6.3 to 3.9.9

---
updated-dependencies:
- dependency-name: org.apache.maven:maven-plugin-api
  dependency-type: direct:production
  update-type: version-update:semver-minor
- dependency-name: org.apache.maven:maven-artifact
  dependency-type: direct:production
  update-type: version-update:semver-minor
- dependency-name: org.apache.maven:maven-core
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

Signed-off-by: dependabot[bot] <[email protected]>

* Preserve required Maven version as 3.6.3

---------

Signed-off-by: dependabot[bot] <[email protected]>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>
Co-authored-by: Slawomir Jaranowski <[email protected]>

pom.xml

@@ -42,7 +42,7 @@ under the License.
   </contributors>
 
   <prerequisites>
-    <maven>${mavenVersion}</maven>
+    <maven>3.6.3</maven>
   </prerequisites>
 
   <scm>
@@ -67,7 +67,7 @@ under the License.
   </distributionManagement>
 
   <properties>
-    <mavenVersion>3.6.3</mavenVersion>
+    <mavenVersion>3.9.9</mavenVersion>
     <plexusCompilerVersion>2.15.0</plexusCompilerVersion>
 
     <groovyVersion>2.4.21</groovyVersion>