[ci] Increase Android and Web sharding (#4493)

Currently most of our Cirrus task runs are about 20 minutes or less, but
there are a few consistent outliers:
- One Android shard takes ~40 minutes, and another takes 25-30.
- The Web platform tests take ~40 minutes.

This increases Android sharding from 4 to 5, and web sharding from 1 (no
sharding) to 2 to improve overall test run times.
diff --git a/.cirrus.yml b/.cirrus.yml
index da354c5..e559339 100644
--- a/.cirrus.yml
+++ b/.cirrus.yml
@@ -174,10 +174,11 @@
     - name: android-platform_tests
       env:
         matrix:
-          PLUGIN_SHARDING: "--shardIndex 0 --shardCount 4"
-          PLUGIN_SHARDING: "--shardIndex 1 --shardCount 4"
-          PLUGIN_SHARDING: "--shardIndex 2 --shardCount 4"
-          PLUGIN_SHARDING: "--shardIndex 3 --shardCount 4"
+          PLUGIN_SHARDING: "--shardIndex 0 --shardCount 5"
+          PLUGIN_SHARDING: "--shardIndex 1 --shardCount 5"
+          PLUGIN_SHARDING: "--shardIndex 2 --shardCount 5"
+          PLUGIN_SHARDING: "--shardIndex 3 --shardCount 5"
+          PLUGIN_SHARDING: "--shardIndex 4 --shardCount 5"
         matrix:
           CHANNEL: "master"
           CHANNEL: "stable"
@@ -229,6 +230,9 @@
     - name: web-platform_tests
       env:
         matrix:
+          PLUGIN_SHARDING: "--shardIndex 0 --shardCount 2"
+          PLUGIN_SHARDING: "--shardIndex 1 --shardCount 2"
+        matrix:
           CHANNEL: "master"
           CHANNEL: "stable"
       install_script: