This PR proposes fixes for some of the workflow issues introduced with #418, and to update the GitHub Actions workflows where appropriate to use recent versions of Xcode, macOS and the Actions plugins.

This ended up being a wonderful confluence of problems to solve, resulting in the following changes:
- macOS 11 runners have been removed (GHA doesn't support them anymore).
- Swift versions prior to 5.7 on platforms other than macOS had to be removed, as the images were conflicting with the actions/checkout action (in reality, all node-based actions would fail on these older images).
- Where possible, base tasks like SwiftLint and CocoaPods verification happen on a macOS 14 Sonoma image running Xcode 15.4 (the latest at the time of authoring).
- CocoaPods needed to be upgraded for visionOS support.
- A few minor SwiftLint violations introduced in recent versions needed to be fixed or disabled.
- I disabled running SwiftLint from within the Xcode project when it detects that it is being built on CI. It seemed unnecessary given it's running in a dedicated workflow.
- Existing workflow jobs will now auto-cancel if a new set of jobs is started on the same branch.

* main:
  GitHub Actions workflow fixes (jpsim#422)
  add os(visionOS) support (jpsim#418)
  Bump rexml from 3.2.5 to 3.2.8

# By JP Simard (3) and others
# Via GitHub
* upstream/main:
  Require Swift 5.7 or later (jpsim#424)
  Add empty changelog section
  Release 5.1.3
  add support for riscv64 (jpsim#419)
  Add support for Android (jpsim#421)
  GitHub Actions workflow fixes (jpsim#422)
  add os(visionOS) support (jpsim#418)
  Bazel: support rules_swift 2.x (jpsim#420)
  Bump rexml from 3.2.5 to 3.2.8

# Conflicts:
#	CHANGELOG.md