Changelog entry for no longer explicitly invoking python2

Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>
diff --git a/ChangeLog.d/make-generate-tests-python.txt b/ChangeLog.d/make-generate-tests-python.txt
new file mode 100644
index 0000000..4b9009d
--- /dev/null
+++ b/ChangeLog.d/make-generate-tests-python.txt
@@ -0,0 +1,3 @@
+Changes
+   * When building the test suites with GNU make, invoke python3 or python, not
+     python2, which is no longer supported upstream.