Unconditionally add the import for assertThrows, got a report where the template adds the method successfully but with missing type attribution for assertThrows so the import was missing

Author: sambsnyd

src/main/java/org/openrewrite/java/testing/junit5/GradleUseJunitJupiter.java

@@ -149,7 +149,8 @@ private static class AddUseJUnitPlatform extends GroovyIsoVisitor<ExecutionConte
         public G.CompilationUnit visitCompilationUnit(G.CompilationUnit cu, ExecutionContext ctx) {
             G.CompilationUnit template = GradleParser.builder()
                     .build()
-                    .parse("plugins {\n" +
+                    .parse(ctx,
+                           "plugins {\n" +
                            "    id 'java'\n" +
                            "}\n" +
                            "tasks.withType(Test).configureEach {\n" +
@@ -235,7 +236,8 @@ public J.Lambda visitLambda(J.Lambda l, ExecutionContext ctx) {
             }
             G.CompilationUnit cu = GradleParser.builder()
                     .build()
-                    .parse("plugins {\n" +
+                    .parse(ctx,
+                           "plugins {\n" +
                            "    id 'java'\n" +
                            "}\n" +
                            "tasks.withType(Test) {\n" +