update-check: fix 'read' exit status

[casperklein]

Description

Currently, the read command fails with exit code 1. That is not an issue, the script continues running.

The problem is, that the delimiter (-d '') is set to a null byte. However, the heredoc does not contain a null byte to terminate.

So this PR changes the delimiter to #, which I also added at the end of the heredoc.

As mentioned, that is currently not an issue. It's just not "clean", having a successful command that signals failure via the exit code. This could be a problem in the future, if we decide to introduce set -e widely.

PS: -d '' is equivalent to -d $'\0'.

-d delim continue until the first character of DELIM is read, rather than newline

Type of change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Improvement (non-breaking change that does improve existing functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• This change requires a documentation update

Checklist:

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation (README.md or the documentation under docs/)
• If necessary I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• I have added information about changes made in this PR to CHANGELOG.md

[casperklein]

fyi: test parallel/set3 failed. Re-running the test set was successful.