Update integration_test iOS FTL README script to remove targeted version (#143248)

1. Remove `dev_target` from suggested Firebase Test Lab iOS script and use wildcard instead.
2. First run `flutter clean` before building to avoid collisions between runs.
3. Use `zip --must-match` in case the xctestrun or `Release-iphoneos` directories are missing (like ran with `--profile` instead of `--release` on purpose) to fail instead of zipping up only part of what's needed.

This came out of a discussion with FTL about these instructions and I tried to run them locally and avoided setting `dev_target`.

See also #74428

Author: jmagman

packages/integration_test/README.md

@@ -311,7 +311,8 @@ Execute this script at the root of your Flutter app:
 ```sh
 output="../build/ios_integ"
 product="build/ios_integ/Build/Products"
-dev_target="14.3"
+
+flutter clean
 
 # Pass --simulator if building for the simulator.
 flutter build ios integration_test/foo_test.dart --release
@@ -327,15 +328,15 @@ xcodebuild build-for-testing \
 popd
 
 pushd $product
-zip -r "ios_tests.zip" "Release-iphoneos" "Runner_iphoneos$dev_target-arm64.xctestrun"
+find . -name "Runner_*.xctestrun" -exec zip -r --must-match "ios_tests.zip" "Release-iphoneos" {} +
 popd
 ```
 
 You can verify locally that your tests are successful by running the following command:
 
 ```sh
 xcodebuild test-without-building \
-  -xctestrun "build/ios_integ/Build/Products/Runner_iphoneos14.3-arm64.xctestrun" \
+  -xctestrun "build/ios_integ/Build/Products/Runner_*.xctestrun" \
   -destination id=<YOUR_DEVICE_ID>
 ```