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.

routers/web/repo/release.go

@@ -185,6 +185,11 @@ func Releases(ctx *context.Context) {
 		ctx.ServerError("getReleaseInfos", err)
 		return
 	}
+	for _, rel := range releases {
+		if rel.Release.IsTag && rel.Release.Title == "" {
+			rel.Release.Title = rel.Release.TagName
+		}
+	}
 
 	ctx.Data["Releases"] = releases
 
@@ -283,6 +288,7 @@ func SingleRelease(ctx *context.Context) {
 		TagNames:    []string{ctx.Params("*")},
 		// only show draft releases for users who can write, read-only users shouldn't see draft releases.
 		IncludeDrafts: writeAccess,
+		IncludeTags:   true,
 	})
 	if err != nil {
 		ctx.ServerError("getReleaseInfos", err)
@@ -294,6 +300,9 @@ func SingleRelease(ctx *context.Context) {
 	}
 
 	release := releases[0].Release
+	if release.IsTag && release.Title == "" {
+		release.Title = release.TagName
+	}
 
 	ctx.Data["PageIsSingleTag"] = release.IsTag
 	if release.IsTag {