[MNG-7743] Make the build work on JDK 20 (#1065)

* [MNG-7743] Make the build work on JDK 20

 * the behaviour before the fix was already pretty confusing. JDK 19 and
   older do not check the presense of '{' in the constructor, so the
   URL object got created, but when converting to file the result would
   be e.g. '/../../src/test/remote-repo' which is completely wrong.
   But it seems the affected tests did not really care, as all of them
   were passing

* Remove forgotten println

Co-authored-by: Yeikel <email@yeikel.com>

* Test with latest JDK

* Do not run ITs with jdk 20, but just the "build itself"

---------

Co-authored-by: Yeikel <email@yeikel.com>
Co-authored-by: Guillaume Nodet <gnodet@gmail.com>
# Conflicts:
#	.github/workflows/maven_build_itself.yml
#	maven-core/src/test/java/org/apache/maven/repository/TestRepositoryConnector.java

maven-core/src/test/java/org/apache/maven/repository/TestRepositoryConnector.java

@@ -49,10 +49,20 @@ public class TestRepositoryConnector implements RepositoryConnector {
 
     public TestRepositoryConnector(RemoteRepository repository) {
         this.repository = repository;
-        try {
-            basedir = FileUtils.toFile(new URL(repository.getUrl()));
-        } catch (MalformedURLException e) {
-            throw new IllegalStateException(e);
+        String repositoryUrl = repository.getUrl();
+        if (repositoryUrl.contains("${")) {
+            // the repository url contains unresolved properties and getting the basedir is not possible
+            // in JDK 20+ 'new URL(string)' will fail if the string contains a curly brace
+            this.basedir = null;
+        } else {
+            try {
+                URL url = new URL(repository.getUrl());
+                if ("file".equals(url.getProtocol())) {
+                    basedir = new File(url.getPath());
+                }
+            } catch (MalformedURLException e) {
+                throw new IllegalStateException(e);
+            }
         }
     }