docs: update build script examples to Gradle 9.0

Author: jwharm

docs/getting-started/getting_started_07.md

@@ -52,11 +52,9 @@ glib-compile-resources exampleapp.gresource.xml
 You can run this automatically before Gradle compiles the application, by adding a custom task to `build.gradle`:
 
 ```groovy
-tasks.register('compileResources') {
-    exec {
-        workingDir 'src/main/resources'
-        commandLine 'glib-compile-resources', 'exampleapp.gresource.xml'
-    }
+tasks.register('compileResources', Exec) {
+    workingDir 'src/main/resources'
+    commandLine 'glib-compile-resources', 'exampleapp.gresource.xml'
 }
 
 tasks.named('classes') {

docs/templates.md

@@ -77,11 +77,9 @@ The path to the UI file is treated by Java-GI as a [GResource](https://docs.gtk.
 === "Gradle (Groovy)"
 
     ```groovy
-    tasks.register('compileResources') {
-        exec {
-            workingDir 'src/main/resources'
-            commandLine 'glib-compile-resources', 'example.gresource.xml'
-        }
+    tasks.register('compileResources', Exec) {
+        workingDir 'src/main/resources'
+        commandLine 'glib-compile-resources', 'example.gresource.xml'
     }
 
     tasks.named('compileJava') {