SwiftLint > 0.59.1 throws ViolationSeverity error

New Issue Checklist

• I've Updated SwiftLint to the latest version.
• I've searched for existing GitHub issues.

Bug Description

A clear and concise description of what the bug is. Ideally, provide a small (but compilable) example code snippet that can be used to reproduce the issue.

When I run swiftlint 0.63.0 (or any version above 0.59.1) via Bazel, e.g.

bazel test //plugins/beacon/swiftui:PlayerUIBeaconPluginSwiftLint

I see this error:

external/swiftlint+/Source/SwiftLintCore/Models/SeverityConfiguration.swift:19:14: error: cannot assign to property: 'severity' is a get-only property
17 |     /// - parameter severity: The severity that should be used when emitting violations.
18 |     public init(_ severity: ViolationSeverity) {
19 |         self.severity = severity
   |              `- error: cannot assign to property: 'severity' is a get-only property
20 |     }
21 | 

external/swiftlint+/Source/SwiftLintCore/Models/SeverityConfiguration.swift:27:22: error: cannot assign to property: 'severity' is a get-only property
25 |         if let severityString: String = configString ?? configDict?[$severity.key] as? String {
26 |             if let severity = ViolationSeverity(rawValue: severityString.lowercased()) {
27 |                 self.severity = severity
   |                      `- error: cannot assign to property: 'severity' is a get-only property
28 |             } else {
29 |                 throw .invalidConfiguration(ruleID: Parent.identifier)

external/swiftlint+/Source/SwiftLintCore/Models/ViolationSeverity.swift:3:13: error: type 'ViolationSeverity' does not conform to protocol 'AcceptableByConfigurationElement'
 1 | /// The magnitude of a `StyleViolation`.
 2 | @AcceptableByConfigurationElement
 3 | public enum ViolationSeverity: String, Comparable, CaseIterable, Codable, Sendable, InlinableOptionType {
   |             `- error: type 'ViolationSeverity' does not conform to protocol 'AcceptableByConfigurationElement'
 4 |     /// Non-fatal. If using SwiftLint as an Xcode build phase, Xcode will mark the build as having succeeded.
 5 |     case warning

I am specifically seeing this with the player-ui repo, in this PR migrating to Xcode 26+. The SwiftLint call is defined in a helper here:

    native.sh_test(
        name = name + "SwiftLint",
        srcs = [":" + name + "_Lint"],
        visibility = ["//visibility:public"],
    )

    # Runs the SwiftLint as part of the build, if lint fails with serious violations defer the results for the test
    native.genrule(
        name = name + "_Lint",
        tools = [
            "@SwiftLint//:swiftlint",
        ],
        srcs = [":" + name + "_Sources"] + ["//:.swiftlint.yml"],
        outs = ["output.sh"],
        executable = True,
        testonly = True,
        visibility = ["//visibility:public"],
        cmd = """
      echo `$(location @SwiftLint//:swiftlint) --config $(location //:.swiftlint.yml) $(SRCS) || true` > lint_results.txt
      LINT=$$(cat lint_results.txt)

      echo '#!/bin/bash' > $(location output.sh)
      echo "echo '$$LINT'" > $(location output.sh)

      LINESWITHERROR=$$(echo grep error lint_results.txt || true)
      echo "exit $$(($$LINESWITHERROR) | wc -l)" >> $(location output.sh)
  """,
    )

Environment

• SwiftLint version (run swiftlint version to be sure): 0.63.0
• Xcode version (run xcodebuild -version to be sure): 26.1 on MacOS 15.7.2
• Installation method used (Homebrew, CocoaPods, building from source, etc): Bazel
• Configuration file:

disabled_rules:
    - unused_optional_binding
    - unused_setter_value
type_name:
    excluded:
        - T
line_length:
    warning: 160
    ignores_comments: true
function_body_length: 50
identifier_name:
    excluded:
        - id
        - file_input
        - text_input
        - check_box
        - drop_down
        - radio_button
        - search_input
included:
    - ios
    - plugins

Are you using nested configurations? If so, paste their
relative paths and respective contents.
Not using.

Reproduce the failure with bazel test //plugins/beacon/swiftui:PlayerUIBeaconPluginSwiftLint and SwiftLint 0.63.0. Start with Source/SwiftLintCore/Models/SeverityConfiguration.swift and ViolationSeverity.swift, then inspect the Bazel invocation in common_utils.bzl. Done means SwiftLint builds and the reported Bazel test runs without the ViolationSeverity conformance and get-only-property errors.