Pre recieve hook block credentials error

After upgrade to 2.20 on GHES, block credentials script throws error when deleting tags on remote server from a local client.
```
git push origin :refs/tags/new
remote: fatal: Invalid revision range 3b5bec62228f296578699964da63b73025357a6b..0000000000000000000000000000000000000000
```

Locate the block credentials pre-receive hook and reproduce the failure with `git push origin :refs/tags/new` on the stated GHES version. Done means remote tag deletion no longer raises the invalid revision range error while credential blocking continues to work.

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