Introduced sha256 support for git-sizer

This is a best practice and yamllint warns about omitting it.

We'd like to run GitHub Actions with the least possible permissions
assigned to the token for security reasons.  To make this possible,
let's add a permissions block to each workflow that lacks one.

Add permissions blocks to workflows that lack them

The Google storage account appears to no longer be valid, so let's use the official download link from https://go.dev.

install-vendored-go: update download link

If you are building and running the tests in an environment with an older
version of git, it might not have SHA256 support. This should not cause the
git-sizer test suite to fail as it's not an issue with git-sizer.

Detect this situation and skip the test.

Version 2 wants to use the old URL so that also fails to run. The latest is
version 6 so let's update to that and at the same time update to the same Go
version that we want to download in the build script.

As pointed out by the robot, this can be an issue with different locales. It is
enough for our purposes to know that the error message includes "object-format"
so we know it's unhappy with it.

Skip the SHA256 test if git has not support for it