Be consistent with tags; add missing releases

I noticed that the Git tags are inconsistent, some starting with `v` and some not. I thought you might have changed formats to include `v` after `6.4.1` but you went back to no prefix for `6.4.10`, and then back again to `v` for `v7.0.0a1`.

It would probably be easier on everyone if you could stick to one format for the tags.

Current tags:

```
v7.0.0a2
v7.0.0a1
6.4.10
v6.4.9
v6.4.8
v6.4.7
v6.4.6
v6.4.5
v6.4.4
v6.4.3
v6.4.2
6.4.1
v6.4.0rc0
v6.4.0
6.3.0
6.2.0
```

older

```
6.1.6
6.1.5
6.1.4
6.1.3
6.1.2
6.1.1
6.1.0rc1
6.1.0
6.0.3
6.0.2
6.0.1
6.0.0rc1
6.0.0
5.7.9
5.7.8
5.7.7
5.7.6
5.7.5
5.7.4
5.7.3
5.7.2
5.7.13
5.7.12
5.7.11
5.7.10
5.7.1
5.7.0
5.6.0rc1
5.6.0
5.5.0rc1
5.5.0
5.4.1
5.4.0
5.3.1
5.3.0rc1
5.3.0
5.2.2
5.2.1rc1
5.2.1
5.2.0rc1
5.2.0
5.1.0rc3
5.1.0rc2
5.1.0rc1
5.1.0
5.0.0rc2
5.0.0b2
5.0.0b1
5.0.0-rc.1
5.0.0
4.x-test
4.4.1
4.4.0
4.3.2
4.3.1
4.3.0
4.2.3
4.2.2
4.2.1
4.2.0
4.1.0
4.0.6
4.0.5
4.0.4
4.0.3
4.0.2
4.0.1
4.0.0
```

In addition, [the releases page](https://github.com/jupyter/notebook/releases) is missing 6.4.9 and 6.4.10.

Start by comparing the repository's Git tags with the releases page linked in the issue, focusing on the inconsistent `v` prefixes and the missing 6.4.9 and 6.4.10 releases. Done means the tag format is consistent and both missing releases are present on GitHub.

Written by the indexing model from the issue text.