Enable gix-dir walk symlink tests even on Windows

As detailed in d715e4a, most tests involving symlinks have been
expected to work even on Windows since #1444, but some tests remain
to be updated to be run on Windows or to include all
symlink-related asertions on Windows.

This includes 4 tests in `gix-dir/tests/walk/mod.rs`, which were
ignored on Windows even though they are able to pass. This commit
enables them on Windows. It also updates the associated fixture
scripts to no longer say that symlink test can't run on Windows.
But no changes to the fixture scripts are required for the tests to
pass.

(While doing so, I've made a small change, adding quoting to a here
document delimiter to make clear that no expansions are intended to
occur in the here document text. But this change is purely for
clarity; nothing was broken in connection with that heredoc.)

gix-dir/tests/fixtures/many-symlinks.sh

@@ -1,8 +1,7 @@
 #!/usr/bin/env bash
 set -eu -o pipefail
 
-# Note that symlink creation fails on Windows for some reason,
-# so these tests shouldn't be run there.
+# These fixtures use symlinks. See `many.sh` for some that don't.
 
 git init breakout-symlink
 (cd breakout-symlink
@@ -20,7 +19,7 @@ git init immediate-breakout-symlink
 
 git init excluded-symlinks-to-dir
 (cd excluded-symlinks-to-dir
-  cat <<EOF >.gitignore
+  cat <<'EOF' >.gitignore
 src1
 src2/
 file1
@@ -42,4 +41,4 @@ EOF
   ln -s src/file file2
 )
 
-ln -s excluded-symlinks-to-dir worktree-root-is-symlink
+ln -s excluded-symlinks-to-dir worktree-root-is-symlink

gix-dir/tests/fixtures/many.sh

@@ -1,7 +1,7 @@
 #!/usr/bin/env bash
 set -eu -o pipefail
 
-# Nothing here may use symlinks so these fixtures can be used on windows as well.
+# These fixtures don't use symlinks. See `many-symlinks.sh` for some that do.
 
 git init with-nested-dot-git
 (cd with-nested-dot-git

gix-dir/tests/walk/mod.rs

@@ -19,7 +19,6 @@ use gix_dir::walk::ForDeletionMode;
 use gix_ignore::Kind::*;
 
 #[test]
-#[cfg_attr(windows, ignore = "symlinks the way they are organized don't yet work on windows")]
 fn symlink_to_dir_can_be_excluded() -> crate::Result {
     let root = fixture_in("many-symlinks", "excluded-symlinks-to-dir");
     let ((out, _root), entries) = collect(&root, None, |keep, ctx| {
@@ -94,7 +93,6 @@ fn symlink_to_dir_can_be_excluded() -> crate::Result {
 }
 
 #[test]
-#[cfg_attr(windows, ignore = "symlinks the way they are organized don't yet work on windows")]
 fn root_may_not_lead_through_symlinks() -> crate::Result {
     for (name, intermediate, expected) in [
         ("immediate-breakout-symlink", "", 0),
@@ -121,7 +119,6 @@ fn root_may_not_lead_through_symlinks() -> crate::Result {
 }
 
 #[test]
-#[cfg_attr(windows, ignore = "symlinks the way they are organized don't yet work on windows")]
 fn root_may_be_a_symlink_if_it_is_the_worktree() -> crate::Result {
     let root = fixture_in("many-symlinks", "worktree-root-is-symlink");
     let ((_out, _root), entries) = collect(&root, None, |keep, ctx| {
@@ -2702,7 +2699,6 @@ fn decomposed_unicode_in_directory_is_returned_precomposed() -> crate::Result {
 }
 
 #[test]
-#[cfg_attr(windows, ignore = "symlinks the way they are organized don't yet work on windows")]
 fn worktree_root_can_be_symlink() -> crate::Result {
     let root = fixture_in("many-symlinks", "symlink-to-breakout-symlink");
     let troot = root.join("file");