Update Minimum Swift Version to 5.6 (#2996)

* Bump manifest to Swift 5.6

* Update README

* Remove old version check

* Trigger new CI

.github/workflows/test.yml

@@ -23,7 +23,7 @@ jobs:
           - provider: vapor/apns
             ref: 3.0.0
     runs-on: ubuntu-latest
-    container: swift:5.7-jammy
+    container: swift:5.8
     steps: 
       - name: Check out Vapor
         uses: actions/checkout@v3

Package.swift

@@ -1,4 +1,4 @@
-// swift-tools-version:5.5.2
+// swift-tools-version:5.6
 import PackageDescription
 
 let package = Package(

README.md

@@ -18,7 +18,7 @@
         <img src="https://github.com/vapor/vapor/actions/workflows/test.yml/badge.svg?branch=main" alt="Continuous Integration">
     </a>
     <a href="https://swift.org">
-        <img src="https://img.shields.io/badge/swift-5.5-brightgreen.svg" alt="Swift 5.5">
+        <img src="https://img.shields.io/badge/swift-5.6-brightgreen.svg" alt="Swift 5.6">
     </a>
     <a href="https://twitter.com/codevapor">
         <img src="https://img.shields.io/badge/twitter-codevapor-5AA9E7.svg" alt="Twitter">

Sources/Vapor/Utilities/BasicCodingKey.swift

@@ -1,4 +1,4 @@
-#if swift(>=5.6) && os(Linux)
+#if os(Linux)
 public typealias CodingKeyRepresentable = Swift.CodingKeyRepresentable
 #else
 /// This is an unwelcome stand-in for the ``Swift/CodingKeyRepresentable`` protocol that appeared in Swift 5.6.