Improve error handling in JDK upgrade checks

[spring-builds]

[wilkinsona]

I think this was opened in error. The CI logged the following:

parse error: Invalid numeric literal at line 2, column 0

That looks like a temporary glitch as the other Java 14 version checks all ran successfully and didn't find anything to upgrade. We should improve the error handling to avoid creating the issue.

[dreis2211]

What about just adding set -e on top? That should probably exit the script before it tries to create the issue. What do you think? I can provide a PR for that.

[wilkinsona]

That would certainly be better than how it behaves at the moment. I was wondering if we should output the response that couldn't be parsed so that we can be sure that it was just a glitch rather than a breaking change in the format of the response.

[dreis2211]

I'm currently playing around with more incremental steps and additional checks. Since I'm hitting that at the moment and I can't see the logs of the build unfortunately to see where it exactly failed: maybe it's related to rate-limiting? This produces another result which can't be parsed.

[wilkinsona]

Closing in favour of #22110.