FileSystemException when executed in not-cloned-to worktree

[pzygielo]

• summary of problem
  When build/check is executed in separate worktree (git worktree add ../${project-worktree-dir}) then FileSystemException is reported as ERROR. This however has no impact on the result of the build fortunately.
  This MIGHT be related to 477475, but I guess can also be handled in GitAttributesLineEndings.
• gradle or maven version
  Apache Maven 3.8.4 (9b656c72d54e5bacbed989b64718c159fe39b537)
• spotless version
  2.18.0
• operating system and version
  Fedora 35
• copy-paste your full Spotless configuration block(s), and a link to a public git repo that reproduces the problem if possible
• copy-paste the full content of any console errors emitted by gradlew spotless[Apply/Check] --stacktrace

[INFO] --- spotless-maven-plugin:2.18.0:check (spotless-validation) @ ... ---
...
[ERROR] .../${project-worktree-dir}/.git/config: Not a directory
java.nio.file.FileSystemException: .../${project-worktree-dir}/.git/config: Not a directory
    at sun.nio.fs.UnixException.translateToIOException (UnixException.java:100)
    at sun.nio.fs.UnixException.rethrowAsIOException (UnixException.java:111)
    at sun.nio.fs.UnixException.rethrowAsIOException (UnixException.java:116)
    at sun.nio.fs.UnixFileAttributeViews$Basic.readAttributes (UnixFileAttributeViews.java:55)
    at sun.nio.fs.UnixFileSystemProvider.readAttributes (UnixFileSystemProvider.java:149)
    at sun.nio.fs.LinuxFileSystemProvider.readAttributes (LinuxFileSystemProvider.java:99)
    at java.nio.file.Files.readAttributes (Files.java:1764)
    at org.eclipse.jgit.util.FileUtils.fileAttributes (FileUtils.java:710)
    at org.eclipse.jgit.util.FS.fileAttributes (FS.java:1247)
    at org.eclipse.jgit.internal.storage.file.FileSnapshot.<init> (FileSnapshot.java:230)
    at org.eclipse.jgit.internal.storage.file.FileSnapshot.saveNoConfig (FileSnapshot.java:120)
    at org.eclipse.jgit.storage.file.FileBasedConfig.load (FileBasedConfig.java:125)
    at com.diffplug.common.base.Errors.lambda$wrap$5 (Errors.java:218)
    at com.diffplug.common.base.Errors.run (Errors.java:210)
    at com.diffplug.spotless.extra.GitAttributesLineEndings$RuntimeInit.<init> (GitAttributesLineEndings.java:193)
    at com.diffplug.spotless.extra.GitAttributesLineEndings$RelocatablePolicy.calculateState (GitAttributesLineEndings.java:89)
    at com.diffplug.spotless.extra.GitAttributesLineEndings$RelocatablePolicy.calculateState (GitAttributesLineEndings.java:76)
    at com.diffplug.spotless.LazyForwardingEquality.state (LazyForwardingEquality.java:56)
    at com.diffplug.spotless.LazyForwardingEquality.toBytes (LazyForwardingEquality.java:85)
    at com.diffplug.spotless.LazyForwardingEquality.hashCode (LazyForwardingEquality.java:102)
    at com.diffplug.spotless.Formatter.hashCode (Formatter.java:252)
    at java.util.HashMap.hash (HashMap.java:340)

[nedtwigg]

Dupe of #75.