#760 Build will have plugin validation issues with Maven 3.9.2+.

Addresses #760

The remaining warnings, using Maven 3.9.6:

[WARNING] 
[WARNING] Plugin [INTERNAL, EXTERNAL] validation issues were detected in following plugin(s)
[WARNING] 
[WARNING]  * org.apache.maven.plugins:maven-checkstyle-plugin:3.3.1
[WARNING]   Plugin EXTERNAL issue(s):
[WARNING]    * Plugin depends on plexus-container-default, which is EOL
[WARNING] 
[WARNING]  * org.apache.maven.plugins:maven-site-plugin:3.12.1
[WARNING]   Plugin EXTERNAL issue(s):
[WARNING]    * Plugin depends on the deprecated Maven 2.x compatibility layer, which will be not supported in Maven 4.x
[WARNING] 
[WARNING]  * ch.mfrey.maven.plugin:copy-maven-plugin:1.0.0
[WARNING]   Plugin EXTERNAL issue(s):
[WARNING]    * Plugin is a Maven 2.x plugin, which will be not supported in Maven 4.x
[WARNING]    * Plugin mixes multiple Maven versions: [3.2.1, 2.2.1]
[WARNING] 
[WARNING]  * org.eclipse.tycho:tycho-surefire-plugin:4.0.5
[WARNING]   Declared at location(s):
[WARNING]    * org.eclipse.escet:org.eclipse.escet.releng.configuration:3.0.0-SNAPSHOT (releng\org.eclipse.escet.releng.configuration\pom.xml) @ line 400
[WARNING]   Mojo EXTERNAL issue(s):
[WARNING]    * Mojo tycho-surefire:plugin-test (org.eclipse.tycho.surefire.TychoIntegrationTestMojo)
[WARNING]      - Parameter 'localRepository' uses deprecated parameter expression '${localRepository}': ArtifactRepository type is deprecated and its use in Mojos should be avoided.
[WARNING] 
[WARNING]  * com.google.code.maven-replacer-plugin:replacer:1.5.3
[WARNING]   Plugin EXTERNAL issue(s):
[WARNING]    * Plugin should declare Maven artifacts in `provided` scope. If the plugin already declares them in `provided` scope, update the maven-plugin-plugin to latest version. Artifacts found with wrong scope: [org.apache.maven:maven-plugin-api:3.0.3]
[WARNING] 
[WARNING] 
[WARNING] Fix reported issues by adjusting plugin configuration or by upgrading above listed plugins. If no upgrade available, please notify plugin maintainers about reported issues.
[WARNING] For more or less details, use 'maven.plugin.validation' property with one of the values (case insensitive): [NONE, INLINE, SUMMARY, BRIEF, VERBOSE]
[WARNING] 

Left:

• maven-checkstyle-plugin, we use the latest version: https://mvnrepository.com/artifact/org.apache.maven.plugins/maven-checkstyle-plugin
• maven-site-plugin. Don't know where we use/import it and how its version is determined.
• copy-maven-plugin, seems to be the latest version: https://mvnrepository.com/artifact/ch.mfrey.maven.plugin/copy-maven-plugin
• tycho-surefire-plugin, this was fixed, we discussed it before here: !606 (comment 1158465), but now it is back again.
• replacer can't find a new version 1.5.3 released on April 16th, 2014: https://code.google.com/archive/p/maven-replacer-plugin/