Use Xcode 14.3.1

This was done to address the following CI failure when building with the
Gutenberg XCFramework:

```
▸ Linking WordPress
⚠️  ld: Could not find or use auto-linked library 'swiftCompatibility56'

❌  ld: symbol(s) not found for architecture x86_64
```

https://buildkite.com/automattic/wordpress-ios/builds/14356#01885545-c05a-43a8-b475-d0d683857672

.buildkite/cache-builder.yml

@@ -14,7 +14,7 @@ common_params:
   # Common environment values to use with the `env` key.
   - &common_env
     # Be sure to also update the `.xcode-version` file when updating the Xcode image/version here
-    IMAGE_ID: xcode-14.2
+    IMAGE_ID: xcode-14.3.1
 
 steps:
 

.buildkite/pipeline.yml

@@ -9,7 +9,7 @@ common_params:
   # Common environment values to use with the `env` key.
   - &common_env
     # Be sure to also update the `.xcode-version` file when updating the Xcode image/version here
-    IMAGE_ID: xcode-14.2
+    IMAGE_ID: xcode-14.3.1
 
 # This is the default pipeline – it will build and test the app
 steps:

.buildkite/release-builds.yml

@@ -11,7 +11,7 @@ common_params:
   # Common environment values to use with the `env` key.
   - &common_env
     # Be sure to also update the `.xcode-version` file when updating the Xcode image/version here
-    IMAGE_ID: xcode-14.2
+    IMAGE_ID: xcode-14.3.1
 
 steps:
 

.xcode-version

@@ -1 +1 @@
-14.2
+14.3.1

Gemfile

@@ -2,7 +2,7 @@
 
 source 'https://rubygems.org'
 
-# 1.12.x and higher, starting from 1.12.1
+# 1.12.x and higher, starting from 1.12.1, because that hotfix fixes Xcode 14.3 compatibility
 gem 'cocoapods', '~> 1.12', '>= 1.12.1'
 gem 'commonmarker'
 gem 'danger', '~> 9.3'