[CP-stable][ci] Increase test timeout for Mac_x64 build_tests shards (#188881)

This pull request is created by [automatic cherry pick workflow](https://github.com/flutter/flutter/blob/main/docs/releases/Flutter-Cherrypick-Process.md#automatically-creates-a-cherry-pick-request)
Please fill in the form below, and a flutter domain expert will evaluate this cherry pick request.

### Issue Link:
What is the link to the issue this cherry-pick is addressing?

https://github.com/flutter/flutter/issues/188242
https://github.com/flutter/flutter/issues/188872

### Impact Description:
What is the impact (ex. visual jank on Samsung phones, app crash, cannot ship an iOS app)?
Does it impact development (ex. flutter doctor crashes when Android Studio is installed),
or the shipping of production apps (the app crashes on launch).
This information is for domain experts and release engineers to understand the consequences of saying yes or no to the cherry pick.

The `Mac_x64 build_tests` shards (especially shard `2_5`) on CI frequently time out because they take close to 29-30 minutes, exceeding the default 30-minute test timeout. This causes flaky test failures on release branches and blocks the CI/release pipeline.

### Changelog Description:
Explain this cherry pick:
* In one line that is accessible to most Flutter developers.
* That describes the state prior to the fix.
* That includes which platforms are impacted.
See [best practices](https://github.com/flutter/flutter/blob/main/docs/releases/Hotfix-Documentation-Best-Practices.md) for examples.

n/a non user facing 

### Workaround:
Is there a workaround for this issue?

< Replace with workaround here >

### Risk:
What is the risk level of this cherry-pick?

### Test Coverage:
Are you confident that your fix is well-tested by automated tests?

### Validation Steps:
What are the steps to validate that this fix works?

run the post submit tests and see if the failures go away.

.ci.yaml

diff --git a/.ci.yaml b/.ci.yaml
index 053f80c..5db8a46 100644
--- a/.ci.yaml
+++ b/.ci.yaml
@@ -3679,6 +3679,7 @@
     timeout: 60
     properties:
       add_recipes_cq: "true"
+      test_timeout_secs: "2700"
       dependencies: >-
         [
           {"dependency": "android_sdk", "version": "version:36v8unmodified"},
@@ -3697,6 +3698,7 @@
     timeout: 60
     properties:
       add_recipes_cq: "true"
+      test_timeout_secs: "2700"
       dependencies: >-
         [
           {"dependency": "android_sdk", "version": "version:36v8unmodified"},
@@ -3715,6 +3717,7 @@
     timeout: 60
     properties:
       add_recipes_cq: "true"
+      test_timeout_secs: "2700"
       dependencies: >-
         [
           {"dependency": "android_sdk", "version": "version:36v8unmodified"},
@@ -3733,6 +3736,7 @@
     timeout: 60
     properties:
       add_recipes_cq: "true"
+      test_timeout_secs: "2700"
       dependencies: >-
         [
           {"dependency": "android_sdk", "version": "version:36v8unmodified"},
@@ -3751,6 +3755,7 @@
     timeout: 60
     properties:
       add_recipes_cq: "true"
+      test_timeout_secs: "2700"
       dependencies: >-
         [
           {"dependency": "android_sdk", "version": "version:36v8unmodified"},