Enable CI tests on beta (#3538)

diff --git a/.cirrus.yml b/.cirrus.yml
index a49a8b1..c732374 100644
--- a/.cirrus.yml
+++ b/.cirrus.yml
@@ -11,6 +11,8 @@
   upgrade_script:
     - flutter channel stable
     - flutter upgrade
+    - flutter channel beta
+    - flutter upgrade
     - flutter channel master
     - flutter upgrade
     - git fetch origin master
@@ -33,6 +35,7 @@
       env:
         matrix:
           CHANNEL: "master"
+          CHANNEL: "beta"
           CHANNEL: "stable"
       test_script:
         # TODO(jackson): Allow web plugins once supported on stable
@@ -44,12 +47,14 @@
       env:
         matrix:
           CHANNEL: "master"
+          CHANNEL: "beta"
           CHANNEL: "stable"
       script: ./script/incremental_build.sh analyze
     - name: build_all_plugins_apk
       env:
         matrix:
           CHANNEL: "master"
+          CHANNEL: "beta"
           CHANNEL: "stable"
       script:
         # TODO(jackson): Allow web plugins once supported on stable
@@ -79,6 +84,7 @@
           PLUGIN_SHARDING: "--shardIndex 3 --shardCount 4"
         matrix:
           CHANNEL: "master"
+          CHANNEL: "beta"
           CHANNEL: "stable"
         MAPS_API_KEY: ENCRYPTED[596a9f6bca436694625ac50851dc5da6b4d34cba8025f7db5bc9465142e8cd44e15f69e3507787753accebfc4910d550]
         GCLOUD_FIREBASE_TESTLAB_KEY: ENCRYPTED[07586610af1fdfc894e5969f70ef2458341b9b7e9c3b7c4225a663b4a48732b7208a4d91c3b7d45305a6b55fa2a37fc4]
@@ -121,6 +127,8 @@
   upgrade_script:
     - flutter channel stable
     - flutter upgrade
+    - flutter channel beta
+    - flutter upgrade
     - flutter channel master
     - flutter upgrade
     - git fetch origin master
@@ -148,6 +156,8 @@
     - sudo gem install cocoapods
     - flutter channel stable
     - flutter upgrade
+    - flutter channel beta
+    - flutter upgrade
     - flutter channel master
     - flutter upgrade
     - git fetch origin master
@@ -162,6 +172,7 @@
       env:
         matrix:
           CHANNEL: "master"
+          CHANNEL: "beta"
           CHANNEL: "stable"
       script:
         # TODO(jackson): Allow web plugins once supported on stable
@@ -180,6 +191,7 @@
           PLUGIN_SHARDING: "--shardIndex 3 --shardCount 4"
         matrix:
           CHANNEL: "master"
+          CHANNEL: "beta"
           CHANNEL: "stable"
         SIMCTL_CHILD_MAPS_API_KEY: ENCRYPTED[596a9f6bca436694625ac50851dc5da6b4d34cba8025f7db5bc9465142e8cd44e15f69e3507787753accebfc4910d550]
       build_script:
diff --git a/script/build_all_plugins_app.sh b/script/build_all_plugins_app.sh
index 7807e6a..399f1f1 100755
--- a/script/build_all_plugins_app.sh
+++ b/script/build_all_plugins_app.sh
@@ -54,13 +54,11 @@
 readonly EXCLUDED=$(IFS=, ; echo "${EXCLUDED_PLUGINS_LIST[*]}")
 
 ALL_EXCLUDED=($EXCLUDED)
-# Exclude nnbd plugins from stable.
+# Exclude nnbd plugins from stable, and conflicting plugins otherwise.
 if [ "$CHANNEL" == "stable" ]; then
   ALL_EXCLUDED=("$EXCLUDED,$EXCLUDED_PLUGINS_FROM_STABLE")
-fi
-# Exclude non-nnbd plugins from master.
-if [ "$CHANNEL" != "stable" ]; then
-  ALL_EXCLUDED=("$EXCLUDED,$EXCLUDED_PLUGINS_FROM_MASTER")
+else
+  ALL_EXCLUDED=("$EXCLUDED,$EXCLUDED_PLUGINS_FOR_NNBD")
 fi
 
 echo "Excluding the following plugins: $ALL_EXCLUDED"
diff --git a/script/nnbd_plugins.sh b/script/nnbd_plugins.sh
index 3e82ac2..a2c22c6 100644
--- a/script/nnbd_plugins.sh
+++ b/script/nnbd_plugins.sh
@@ -48,4 +48,4 @@
 )
 
 export EXCLUDED_PLUGINS_FROM_STABLE=$(IFS=, ; echo "${NNBD_PLUGINS_LIST[*]}")
-export EXCLUDED_PLUGINS_FROM_MASTER=$(IFS=, ; echo "${NON_NNBD_PLUGINS_LIST[*]}")
+export EXCLUDED_PLUGINS_FOR_NNBD=$(IFS=, ; echo "${NON_NNBD_PLUGINS_LIST[*]}")