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.
diff --git a/.cirrus.yml b/.cirrus.yml
index 33863a3..a1f055b 100644
--- a/.cirrus.yml
+++ b/.cirrus.yml
@@ -37,7 +37,7 @@
     - 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