Fix gradle project convention deprecation

* this is deprecated since gradle 7.1 and will be removed with gradle 9

src/main/java/org/sonarqube/gradle/SonarPropertyComputer.java

@@ -56,6 +56,7 @@
 import org.gradle.api.plugins.JavaBasePlugin;
 import org.gradle.api.plugins.JavaPlugin;
 import org.gradle.api.plugins.JavaPluginConvention;
+import org.gradle.api.plugins.JavaPluginExtension;
 import org.gradle.api.provider.Property;
 import org.gradle.api.provider.Provider;
 import org.gradle.api.reporting.Report;
@@ -430,15 +431,15 @@ private static void configureTestReports(Test testTask, Map<String, Object> prop
   }
 
   private static void configureSourceDirsAndJavaClasspath(Project project, Map<String, Object> properties, boolean addForGroovy) {
-    JavaPluginConvention javaPluginConvention = new DslObject(project).getConvention().getPlugin(JavaPluginConvention.class);
+    JavaPluginExtension javaPluginExtension = project.getExtensions().getByType(JavaPluginExtension.class);
 
-    SourceSet main = javaPluginConvention.getSourceSets().getAt("main");
+    SourceSet main = javaPluginExtension.getSourceSets().getAt("main");
     Collection<File> sourceDirectories = getJavaSourceFiles(main);
     if (sourceDirectories != null) {
       SonarUtils.appendSourcesProp(properties, sourceDirectories, false);
     }
 
-    SourceSet test = javaPluginConvention.getSourceSets().getAt("test");
+    SourceSet test = javaPluginExtension.getSourceSets().getAt("test");
     Collection<File> testDirectories = getJavaSourceFiles(test);
     if (testDirectories != null) {
       SonarUtils.appendSourcesProp(properties, testDirectories, true);
@@ -453,14 +454,14 @@ private static void configureSourceDirsAndJavaClasspath(Project project, Map<Str
   }
 
   private static void configureJavaClasspath(Project project, Map<String, Object> properties, boolean addForGroovy) {
-    JavaPluginConvention javaPluginConvention = new DslObject(project).getConvention().getPlugin(JavaPluginConvention.class);
+    JavaPluginExtension javaPluginExtension = project.getExtensions().getByType(JavaPluginExtension.class);
 
-    SourceSet main = javaPluginConvention.getSourceSets().getAt("main");
+    SourceSet main = javaPluginExtension.getSourceSets().getAt("main");
     Collection<File> mainClassDirs = getJavaOutputDirs(main);
     Collection<File> mainLibraries = getJavaLibraries(main);
     setMainClasspathProps(properties, mainClassDirs, mainLibraries, addForGroovy);
 
-    SourceSet test = javaPluginConvention.getSourceSets().getAt("test");
+    SourceSet test = javaPluginExtension.getSourceSets().getAt("test");
     Collection<File> testClassDirs = getJavaOutputDirs(test);
     Collection<File> testLibraries = getJavaLibraries(test);
     setTestClasspathProps(properties, testClassDirs, testLibraries);