VCS: Fix weird tag creation

VCS: Fix weird tag creation

Creating a tag with an arbitrary user-supplied name can cause problems.
If we fetch, we can just use `FETCH_HEAD` as the ref name directly!

```
Running: git fetch origin d1dc91fd977bb4b28f0e01966fa08640a1283318
From /private/var/folders/z5/fclwwdms3r1gq4k4p3pkvvc00000gn/T/vcstest-90401/src
 * branch            d1dc91fd977bb4b28f0e01966fa08640a1283318 -> FETCH_HEAD

Running: git tag -f d1dc91fd977bb4b28f0e01966fa08640a1283318 FETCH_HEAD

Running: git reset --hard d1dc91fd977bb4b28f0e01966fa08640a1283318 --
warning: refname 'd1dc91fd977bb4b28f0e01966fa08640a1283318' is ambiguous.
Git normally never creates a ref that ends with 40 hex characters
because it will be ignored when you just specify 40-hex. These refs
may be created by mistake. For example,

  git switch -c $br $(git rev-parse ...)

where "$br" is somehow empty and a 40-hex ref is created. Please
examine these refs and maybe delete them. Turn this message off by
running "git config advice.objectNameWarning false"
```