ci(apple): explicitly select Xcode 26.0 (#10511)

In order to build the iOS app with the Xcode version that is installed
on the GitHub runners, we need to select the Xcode version by major and
minor version. Currently, the iOS builds are failing because Xcode 26.1
also exists but iOS 26.1 isn't supported (or released?).

See
https://github.com/firezone/firezone/actions/runs/18239282351/job/51938727311.

.github/workflows/_swift.yml

@@ -28,7 +28,7 @@ jobs:
     needs: update-release-draft
     runs-on: macos-15
     env:
-      XCODE_MAJOR: 26
+      XCODE_VERSION: "26.0"
     permissions:
       contents: write # for attaching the build artifacts to the release
       id-token: write

scripts/build/lib.sh

@@ -10,7 +10,7 @@ function setup_runner() {
     local ne_profile_file="$4"
 
     # Use the latest version of Xcode - matches what we typically use for development
-    sudo xcode-select --switch "$(ls -d /Applications/Xcode*${XCODE_MAJOR}*.app | sort -V | tail -n 1)"
+    sudo xcode-select --switch "$(ls -d /Applications/Xcode*${XCODE_VERSION}*.app | sort -V | tail -n 1)"
 
     profiles_path="$HOME/Library/Developer/Xcode/UserData/Provisioning Profiles"
     keychain_pass=$(openssl rand -base64 32)