Remove deprecated usage of buildDir (#3068)

It's replaced with `layout.buildDirectory` in Gradle 8.3

gradle/java-publication.gradle

@@ -99,7 +99,7 @@ publishing {
     }
 
     //useful for testing - running "publish" will create artifacts/pom in a local dir
-    repositories { maven { url = "$buildDir/repo" } }
+    repositories { maven { url = layout.buildDirectory.dir("repo") } }
 }
 
 plugins.withId("java") {

gradle/mockito-core/javadoc.gradle

@@ -9,7 +9,7 @@ javadoc {
     // see https://docs.oracle.com/javase/8/docs/technotes/tools/windows/javadoc.html
 
     source = sourceSets.main.allJava
-    destinationDir = file("$buildDir/javadoc")
+    destinationDir = layout.buildDirectory.dir("javadoc").get().asFile
     title = "Mockito ${project.version} API"
 
     // The way *gradle* javadoc task works and due to *gradle exclusion* the log output triggers javadoc warning and
@@ -57,7 +57,7 @@ javadoc {
     doLast {
         copy {
             from "src/javadoc"
-            into "$buildDir/javadoc"
+            into layout.buildDirectory.dir("javadoc")
         }
     }
 }

gradle/retry-test.gradle

@@ -45,7 +45,7 @@ test {
     }
     afterSuite { descriptor, result ->
         if (!descriptor.parent) { //root
-            def failuresReport = new File(buildDir, name + "-failures.txt")
+            def failuresReport = layout.buildDirectory.file(name + "-failures.txt").get().asFile
             def deletion = !failuresReport.exists() || failuresReport.delete()
             if (!deletion) {
                 throw new GradleException("Problems deleting failures file: $reportPath. Please delete manually and retry.")