style: satisfy markdownlint on #2150 notes

Why: CI pre-commit failed on markdownlint auto-fixes for the issue notes file.

Author: OpenSourceMaintenance-Luccc-grok-4.5

tests/issues/test_2150_shutdown_terminates_sessions.md

@@ -1,6 +1,6 @@
 # Issue #2150 local verification notes
 
-Upstream: https://github.com/modelcontextprotocol/python-sdk/issues/2150
+Upstream: <https://github.com/modelcontextprotocol/python-sdk/issues/2150>
 SHA baseline: 3a6f2996cdd8358957479791e8b26198c07d6a75
 
 ## Bug (still present on main at scout time)