Update minimum version of OpenAPIKit to 3.1.2 (#439)

### Motivation

This picks up a bug fix with inferred properties. While Swift package
resolution should pick this up for adopters automatically, we want to go
into 1.0 with the minimum version of the dependency bumped to one that
includes the fix.

### Modifications

Update minimum version of OpenAPIKit to 3.1.2

### Result

Requires newer OpenAPIKit with fix.

### Test Plan

CI.

Author: simonjbeaumont

Package.swift

@@ -51,7 +51,7 @@ let package = Package(
         .package(url: "https://github.com/apple/swift-algorithms", from: "1.0.0"),
 
         // Read OpenAPI documents
-        .package(url: "https://github.com/mattpolzin/OpenAPIKit.git", from: "3.1.0"),
+        .package(url: "https://github.com/mattpolzin/OpenAPIKit.git", from: "3.1.2"),
         .package(url: "https://github.com/jpsim/Yams.git", "4.0.0"..<"6.0.0"),
 
         // CLI Tool

Tests/OpenAPIGeneratorReferenceTests/CompatabilityTest.swift

@@ -58,7 +58,8 @@ final class CompatibilityTest: XCTestCase {
             "https://raw.githubusercontent.com/box/box-openapi/5955d651f0cd273c0968e3855c1d873c7ae3523e/openapi.json",
             license: .apache,
             expectedDiagnostics: [
-                "Multipart request bodies must always be required, but found an optional one - skipping. Mark as `required: true` to get this body generated."
+                "Multipart request bodies must always be required, but found an optional one - skipping. Mark as `required: true` to get this body generated.",
+                "A property name only appears in the required list, but not in the properties map - this is likely a typo; skipping this property.",
             ],
             skipBuild: compatibilityTestSkipBuild
         )
@@ -98,7 +99,9 @@ final class CompatibilityTest: XCTestCase {
         try await _test(
             "https://raw.githubusercontent.com/github/rest-api-description/13c873cb3b15ffd5bcd88c6d6270a963ef4518f6/descriptions/api.github.com/api.github.com.yaml",
             license: .mit,
-            expectedDiagnostics: [],
+            expectedDiagnostics: [
+                "A property name only appears in the required list, but not in the properties map - this is likely a typo; skipping this property."
+            ],
             skipBuild: true
         )
     }
@@ -108,7 +111,8 @@ final class CompatibilityTest: XCTestCase {
             "https://raw.githubusercontent.com/github/rest-api-description/13c873cb3b15ffd5bcd88c6d6270a963ef4518f6/descriptions/ghes-3.5/ghes-3.5.yaml",
             license: .mit,
             expectedDiagnostics: [
-                "Multipart request bodies must always be required, but found an optional one - skipping. Mark as `required: true` to get this body generated."
+                "Multipart request bodies must always be required, but found an optional one - skipping. Mark as `required: true` to get this body generated.",
+                "A property name only appears in the required list, but not in the properties map - this is likely a typo; skipping this property.",
             ],
             skipBuild: true
         )
@@ -127,7 +131,9 @@ final class CompatibilityTest: XCTestCase {
         try await _test(
             "https://raw.githubusercontent.com/Netflix/consoleme/774420462b0190b1bfa78aa73d39e20044f52db9/swagger.yaml",
             license: .apache,
-            expectedDiagnostics: [],
+            expectedDiagnostics: [
+                "A property name only appears in the required list, but not in the properties map - this is likely a typo; skipping this property."
+            ],
             skipBuild: compatibilityTestSkipBuild
         )
     }