System.IO.IOException: The process cannot access the file 'C:\Users\dte\AppData\Roaming\FancyWM\themes\custom.css' because it is being used by another process.

[ReneMuala]

Describe the bug
Observing the following error:

System.IO.IOException: The process cannot access the file 'C:\Users\dte\AppData\Roaming\FancyWM\themes\custom.css' because it is being used by another process.
   at Microsoft.Win32.SafeHandles.SafeFileHandle.CreateFile(String fullPath, FileMode mode, FileAccess access, FileShare share, FileOptions options)
   at Microsoft.Win32.SafeHandles.SafeFileHandle.Open(String fullPath, FileMode mode, FileAccess access, FileShare share, FileOptions options, Int64 preallocationSize, Nullable`1 unixCreateMode)
   at System.IO.File.OpenHandle(String path, FileMode mode, FileAccess access, FileShare share, FileOptions options, Int64 preallocationSize)
   at System.IO.File.WriteToFile(String path, FileMode mode, ReadOnlySpan`1 contents, Encoding encoding)
   at System.IO.File.WriteAllText(String path, String contents, Encoding encoding)
   at FancyWM.Utilities.ThemeEngineManager.EnsureCustomThemeFileExists()
   at FancyWM.Utilities.ThemeEngineManager.SetTheme(String themeFileName)
   at FancyWM.Utilities.ThemeEngineManager.Initialize(String themeDir, String themeFileName)
   at FancyWM.MainWindow..ctor()
   at System.RuntimeType.CreateInstanceDefaultCtor(Boolean publicOnly, Boolean wrapExceptions)

To Reproduce
Steps to reproduce the behavior:

1. Open '...'
2. Resize '....'
3. Enable '....'
4. See error

Expected behavior
A clear and concise description of what you expected to happen.

Desktop (please complete the following information):

• OS: Microsoft Windows NT 10.0.26200.0
• FancyWM Version: 2.19.0.0

Additional context
Add any other context about the problem here.