WIP: Test API breakage baseline

Author: ahoppen

.github/workflows/pull_request.yml

@@ -10,9 +10,10 @@ jobs:
     uses: swiftlang/github-workflows/.github/workflows/swift_package_test.yml@main
   soundness:
     name: Soundness
-    uses: swiftlang/github-workflows/.github/workflows/soundness.yml@main
+    uses: ahoppen/github-workflows/.github/workflows/soundness.yml@api-breakage-baseline
     with:
-      api_breakage_check_allowlist_path: "Release Notes/api-breakages.txt"
+      api_breakage_check_allowlist_path: "api-breakages.txt"
+      api_breakage_check_baseline: "600.0.1"
       docs_check_additional_arguments: "--disable-parameters-and-returns-validation"
   verify_source_code:
     name: Validate generated code

Sources/SwiftDiagnostics/DiagnosticsFormatter.swift

@@ -367,7 +367,7 @@ public struct DiagnosticsFormatter {
   ///   - leadingText: text that is prefixed to the list of categories when
   ///     there is at least one category to print.
   public func categoryFootnotes(
-    _ categories: [DiagnosticCategory],
+    _ categories: some Sequence<DiagnosticCategory>,
     leadingText: String = "\n"
   ) -> String {
     let categoriesInOrder = categories.compactMap { category in