increase sharding of Windows build_tests (#156763)

Fixes https://github.com/flutter/flutter/issues/156762

<details>

<summary> Pre-launch checklist </summary> 

</details>

.ci.yaml

@@ -5313,7 +5313,8 @@ targets:
       - bin/**
       - .ci.yaml
 
-  - name: Windows build_tests_1_7
+  - name: Windows build_tests_1_8
+    bringup: true
     recipe: flutter/flutter_drone
     timeout: 60
     properties:
@@ -5327,11 +5328,12 @@ targets:
           {"dependency": "vs_build", "version": "version:vs2019"}
         ]
       shard: build_tests
-      subshard: "1_7"
+      subshard: "1_8"
       tags: >
         ["framework", "hostonly", "shard", "windows"]
 
-  - name: Windows build_tests_2_7
+  - name: Windows build_tests_2_8
+    bringup: true
     recipe: flutter/flutter_drone
     timeout: 60
     properties:
@@ -5345,11 +5347,12 @@ targets:
           {"dependency": "vs_build", "version": "version:vs2019"}
         ]
       shard: build_tests
-      subshard: "2_7"
+      subshard: "2_8"
       tags: >
         ["framework", "hostonly", "shard", "windows"]
 
-  - name: Windows build_tests_3_7
+  - name: Windows build_tests_3_8
+    bringup: true
     recipe: flutter/flutter_drone
     timeout: 60
     properties:
@@ -5363,11 +5366,12 @@ targets:
           {"dependency": "vs_build", "version": "version:vs2019"}
         ]
       shard: build_tests
-      subshard: "3_7"
+      subshard: "3_8"
       tags: >
         ["framework", "hostonly", "shard", "windows"]
 
-  - name: Windows build_tests_4_7
+  - name: Windows build_tests_4_8
+    bringup: true
     recipe: flutter/flutter_drone
     timeout: 60
     properties:
@@ -5381,11 +5385,12 @@ targets:
           {"dependency": "vs_build", "version": "version:vs2019"}
         ]
       shard: build_tests
-      subshard: "4_7"
+      subshard: "4_8"
       tags: >
         ["framework", "hostonly", "shard", "windows"]
 
-  - name: Windows build_tests_5_7
+  - name: Windows build_tests_5_8
+    bringup: true
     recipe: flutter/flutter_drone
     timeout: 60
     properties:
@@ -5399,11 +5404,12 @@ targets:
           {"dependency": "vs_build", "version": "version:vs2019"}
         ]
       shard: build_tests
-      subshard: "5_7"
+      subshard: "5_8"
       tags: >
         ["framework", "hostonly", "shard", "windows"]
 
-  - name: Windows build_tests_6_7
+  - name: Windows build_tests_6_8
+    bringup: true
     recipe: flutter/flutter_drone
     timeout: 60
     properties:
@@ -5417,11 +5423,12 @@ targets:
           {"dependency": "vs_build", "version": "version:vs2019"}
         ]
       shard: build_tests
-      subshard: "6_7"
+      subshard: "6_8"
       tags: >
         ["framework", "hostonly", "shard", "windows"]
 
-  - name: Windows build_tests_7_7
+  - name: Windows build_tests_7_8
+    bringup: true
     recipe: flutter/flutter_drone
     timeout: 60
     properties:
@@ -5435,7 +5442,26 @@ targets:
           {"dependency": "vs_build", "version": "version:vs2019"}
         ]
       shard: build_tests
-      subshard: "7_7"
+      subshard: "7_8"
+      tags: >
+        ["framework", "hostonly", "shard", "windows"]
+
+  - name: Windows build_tests_8_8
+    bringup: true
+    recipe: flutter/flutter_drone
+    timeout: 60
+    properties:
+      add_recipes_cq: "true"
+      dependencies: >-
+        [
+          {"dependency": "android_sdk", "version": "version:33v6"},
+          {"dependency": "chrome_and_driver", "version": "version:125.0.6422.141"},
+          {"dependency": "open_jdk", "version": "version:17"},
+          {"dependency": "goldctl", "version": "git_revision:2387d6fff449587eecbb7e45b2692ca0710b63b9"},
+          {"dependency": "vs_build", "version": "version:vs2019"}
+        ]
+      shard: build_tests
+      subshard: "8_8"
       tags: >
         ["framework", "hostonly", "shard", "windows"]