The format of the release checksum does not comply with the standard

[smuu]

Describe the bug
Checking the release_checksum on alpine-based images fails.
The --release parameter in the build command creates a release_checksum file. The content looks like the following <sha256sum><space><file_name>. See here in the code.
From the sha256sum man page: See here.

The sums are computed as described in FIPS-180-2. When checking, the input should be a former output of this program. The default mode is to print a line with checksum, a character indicating type ('*' for binary, ' ' for text), and name for each FILE.

So, in this case, the content of the checksum file should be <sha256sum><space><space><file_name>.
Alpine is very strict when it comes to checking the format of checksums. Debian-based images tolerate this, so it does not fail there.
To reproduce
Steps to reproduce the behavior:

1. Download example releases and checksum file

wget https://github.com/ignite/example/releases/download/latest/release_checksum
wget https://github.com/ignite/example/releases/download/latest/example_latest_darwin_amd64.tar.gz
wget https://github.com/ignite/example/releases/download/latest/example_latest_darwin_arm64.tar.gz
wget https://github.com/ignite/example/releases/download/latest/example_latest_linux_amd64.tar.gz

2. Start an Alpine container and mount the files

docker run -it -w /work -v ./:/work alpine

3. Run the checksum check and see that it fails

cat release_checksum | sha256sum -c -w -

Output:

sha256sum: invalid format
sha256sum: invalid format
sha256sum: invalid format
sha256sum: WARNING: 3 of 3 computed checksums did NOT match

As a reference, this is how it looks for Debian-based images:

cat release_checksum | sha256sum -c -w -

Output:

example_latest_darwin_amd64.tar.gz: OK
example_latest_darwin_arm64.tar.gz: OK
example_latest_linux_amd64.tar.gz: OK

What version are you using?
All versions, code was not changed since it was introduced.