fix(git): keep leading dashes in git grep search patterns (#39404)

Co-authored-by: silverwind <me@silverwind.io>
Co-authored-by: wxiaoguang <wxiaoguang@gmail.com>

modules/git/grep_test.go

@@ -79,6 +79,11 @@ func TestGrepSearch(t *testing.T) {
 	assert.NoError(t, err)
 	assert.Empty(t, res)
 
+	// search a string starting with a dash
+	res, err = GrepSearch(t.Context(), repo, "-v", GrepOptions{})
+	assert.NoError(t, err)
+	assert.Equal(t, []*GrepResult{{Filename: ".gitattributes", LineNumbers: []int{1}, LineCodes: []string{"*.vendor.java linguist-vendored"}}}, res)
+
 	nonExistingRepo := &Repository{RepositoryBase: RepositoryBase{repoFacade: gitrepo.RepositoryUnmanaged("no-such-git-repo")}}
 	res, err = GrepSearch(t.Context(), nonExistingRepo, "no-such-content", GrepOptions{})
 	assert.Error(t, err)