Fix release_rc.sh, use the right artifact file name

[kevinjqliu]

#204

While running release_rc.sh for RC2, I noticed that the .asc file was not generated.
There's a bug in the script similar to #199 and #202 where the filename does not include the RC version.

This PR fixes the script to use the correct file name, apache-iceberg-go-0.1.0-rc2.tar.gz, which corresponds with the artifacts here https://github.com/apache/iceberg-go/releases/tag/v0.1.0-rc2

Tested in terminal

version=0.1.0                            
rc=2
id="apache-iceberg-go-${version}-rc${rc}" 
tar_gz="${id}.tar.gz"
echo $tar_gz
> apache-iceberg-go-0.1.0-rc2.tar.gz

[zeroshade]

LGTM thanks!

[kevinjqliu]

@Fokko can you help with merging this pr?