Update uv language_spec deprecated test to use Python 3.9

Match the same change from python/spec in #15058 — deprecated version
is now 3.9, not 3.8.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: kbukum1

uv/spec/dependabot/uv/language_spec.rb

@@ -22,7 +22,7 @@
     end
 
     context "when detected version is deprecated but not unsupported" do
-      let(:detected_version) { "3.8.1" }
+      let(:detected_version) { "3.9.1" }
 
       before do
         allow(language).to receive(:unsupported?).and_return(false)