Update test runners to use explicit iOS 18.6 version (keyboards are not appearing on iOS 18 sim)

Author: w-goog

.github/workflows/integration_tests.yml

@@ -76,7 +76,7 @@ jobs:
           test-without-building \
           -scheme DaysUntilBirthday\ \(iOS\) \
           -sdk iphonesimulator \
-          -destination 'platform=iOS Simulator,name=iPhone 16' \
+          -destination 'platform=iOS Simulator,name=iPhone 16,OS=18.6' \
           EMAIL_SECRET=$EMAIL_SECRET \
           PASSWORD_SECRET=$PASSWORD_SECRET
 
@@ -109,6 +109,6 @@ jobs:
           test-without-building \
           -scheme AppAttestExample \
           -sdk iphonesimulator \
-          -destination 'platform=iOS Simulator,name=iPhone 16' \
+          -destination 'platform=iOS Simulator,name=iPhone 16,OS=18.6' \
           AppCheckDebugToken=$AppCheckDebugToken \
           APP_CHECK_WEB_API_KEY=$APP_CHECK_WEB_API_KEY