Go 1.25.3 release is botched at Google

["Böszörményi Zoltán" <zboszor@gmail.com>]

Hi,

apparently, the pre-built Go 1.25.3 release, both the
* prebuilt tarballs at https://goloang.org/dl, and
* source tarball at https://dl.google.com/go
are compressed twice with gzip but is named as tar.gz instead of tar.gz.gz

Therefore, the checksums are incorrect, and the downloaded
file cannot be uncompressed with a single tar xzf command.

Uncompressing the tarballs once with gzip makes them match
the expected checksum and can be extracted with tar xvf.

Adding downloadfilename=<basename>.tar.gz.gz makes it download
and extract ONCE, so the result is the <basename>.tar.gz tarball file
instead of the extracted sources or prebuilt stuff.