bug: Worktree.AddGlob adds .git/HEAD

[jiping-s]

version: v5.4.2

Worktree.AddGlob("*") includes .git files that shouldn't be there, e.g.

repo, err := git.PlainInit("newRepo", false)
wt, _ := repo.Worktree()
// create some files
wt.AddGlob("*"))
_, err = wt.Commit("initial commit", &git.CommitOptions{Author: &author})
// now .git/HEAD is part of the repo!

git show b880d9e428bfc2948fbd2b0cf2b0f4e43576834f
commit b880d9e428bfc2948fbd2b0cf2b0f4e43576834f
Author: foo <foo@dotcom>
Date:   Tue Aug 23 16:57:22 2022 +0300

    initial commit

diff --git a/.git/HEAD b/.git/HEAD
new file mode 100644
index 0000000..cb089cd
--- /dev/null
+++ b/.git/HEAD
@@ -0,0 +1 @@
+ref: refs/heads/master
diff --git a/.git/objects/cb/089cd89a7d7686d284d8761201649346b5aa1c b/.git/objects/cb/089cd89a7d7686d284d8761201649346b5aa1c
new file mode 100644
index 0000000..ed4e0ce
Binary files /dev/null and b/.git/objects/cb/089cd89a7d7686d284d8761201649346b5aa1c differ
...
...

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