remove unnecessary new lines in the test

resolves https://github.com/opf/openproject/pull/19449#discussion_r2195651639

spec/models/work_package/pdf_export/common/macro_spec.rb

@@ -125,7 +125,7 @@ RSpec.describe WorkPackage::PDFExport::Common::Macro do
     end
 
     describe "with markdown formating bold" do
-      let(:markdown) { "\n**##{work_package.id}**\n" }
+      let(:markdown) { "**##{work_package.id}**" }
 
       it "contains correct data" do
         expect(formatted).to eq("**#{expected_tag}**")