patch 9.0.0596: CI on Mac M1 has the channel feature disabled

Problem:    CI on Mac M1 has the channel feature disabled.
Solution:   Include the channel feature.

.cirrus.yml

@@ -37,7 +37,7 @@ macos_task:
     - brew install gettext libtool
   build_script:
     - NPROC=$(getconf _NPROCESSORS_ONLN)
-    - ./configure --with-features=${FEATURES} --disable-channel
+    - ./configure --with-features=${FEATURES}
     - make -j${NPROC} CC=clang
   test_script:
     - src/vim --version

src/version.c

@@ -699,6 +699,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    596,
 /**/
     595,
 /**/