Add changelog entry for code/source changes

Author: bluetech

changelog/7438.breaking.rst

@@ -0,0 +1,11 @@
+Some changes were made to the internal ``_pytest._code.source``, listed here
+for the benefit of plugin authors who may be using it:
+
+- The ``deindent`` argument to ``Source()`` has been removed, now it is always true.
+- Support for zero or multiple arguments to ``Source()`` has been removed.
+- Support for comparing ``Source`` with an ``str`` has been removed.
+- The methods ``Source.isparseable()`` and ``Source.putaround()`` have been removed.
+- The method ``Source.compile()`` and function ``_pytest._code.compile()`` have
+  been removed; use plain ``compile()`` instead.
+- The function ``_pytest._code.source.getsource()`` has been removed; use
+  ``Source()`` directly instead.