ContainerRegistry: Don't escape slashes in MIME types (#143)

Motivation
----------

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the problem you're trying to solve.]_

Modifications
-------------

_[Describe the modifications you've made.]_

Result
------

_[After your change, what will change.]_

Test Plan
---------

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such as adjusting tests and manual testing.]_

Author: euanh

Sources/ContainerRegistry/ImageManifest+Digest.swift

@@ -18,7 +18,7 @@ import struct Crypto.SHA256
 public extension ImageManifest {
     var digest: String {
         let encoder = JSONEncoder()
-        encoder.outputFormatting = [.sortedKeys, .prettyPrinted]
+        encoder.outputFormatting = [.sortedKeys, .prettyPrinted, .withoutEscapingSlashes]
         encoder.dateEncodingStrategy = .iso8601
         let encoded = try! encoder.encode(self)
         return ContainerRegistry.digest(of: encoded)

Sources/ContainerRegistry/RegistryClient.swift

@@ -84,7 +84,7 @@ public struct RegistryClient {
             self.encoder = encoder
         } else {
             self.encoder = JSONEncoder()
-            self.encoder.outputFormatting = [.sortedKeys, .prettyPrinted]
+            self.encoder.outputFormatting = [.sortedKeys, .prettyPrinted, .withoutEscapingSlashes]
             self.encoder.dateEncodingStrategy = .iso8601
         }