Limit reshim to current Ruby version

If you have a lot of ruby versions installed, the reshim in:

https://github.com/asdf-vm/asdf-ruby/blob/6b1e7ea906e6980e42dbf35e778e5313711526c4/rubygems-plugin/rubygems_plugin.rb#L2-L7

that is triggered on every `bundle update` - can get really slow:

```
$ time asdf reshim ruby

________________________________________________________
Executed in 22.94 secs fish external
usr time 7.65 secs 425.00 micros 7.65 secs
sys time 10.64 secs 878.00 micros 10.64 secs
```

Limiting the reshim to the current version would make it orders of magnitude faster:

```
$ time asdf reshim ruby 3.4.5

________________________________________________________
Executed in 1.07 secs fish external
usr time 380.67 millis 365.00 micros 380.31 millis
sys time 474.90 millis 938.00 micros 473.97 millis
```