Fix a bug returning 404 when display a single tag with no release (#29466)

Partially caused by #29149 

When use

```go
releases, err := getReleaseInfos(ctx, &repo_model.FindReleasesOptions{
		ListOptions: db.ListOptions{Page: 1, PageSize: 1},
		RepoID:      ctx.Repo.Repository.ID,
		TagNames:    []string{ctx.Params("*")},
		// only show draft releases for users who can write, read-only users shouldn't see draft releases.
		IncludeDrafts: writeAccess,
	})
```
replace
```go
release, err := repo_model.GetRelease(ctx, ctx.Repo.Repository.ID, ctx.Params("*"))
```
It missed `IncludeTags: true,`. That means this bug will be occupied only when the release is a tag.
This PR will fix

 - Get the right tag record when it's not a release
 - Display correct tag tab but not release tag when it's a tag.
- The button will bring the tag name to the new page when it's a single tag page
- the new page will automatically hide the release target inputbox when the tag name is pre filled. This should be backport to v1.21.

tests/integration/links_test.go

@@ -36,6 +36,7 @@ func TestLinksNoLogin(t *testing.T) {
 		"/user2/repo1/",
 		"/user2/repo1/projects",
 		"/user2/repo1/projects/1",
+		"/user2/repo1/releases/tag/delete-tag", // It's the only one existing record on release.yml which has is_tag: true
 		"/assets/img/404.png",
 		"/assets/img/500.png",
 		"/.well-known/security.txt",