Improve the summary of Jenkins emails on failure [LUCENE-9598]

Where are the patterns that drive what's extracted from the console logs sent to builds mailing list? I think these could be improved to include more context starting after "FAILURE" - then you know which task failed exactly, not just that the build failed.

```Java
FAILURE: Build failed with an exception.

* What went wrong:
Execution failed for task ':solr:solr-ref-guide:checkLocalJavadocLinksSite'.
> Process 'command '/usr/local/asfpackages/java/jdk-11.0.6/bin/java'' finished with non-zero exit value 255

* Try:
Run with --stacktrace option to get the stack trace. Run with --info or --debug option to get more log output. Run with --scan to get full insights.

* Get more help at https://help.gradle.org

Deprecated Gradle features were used in this build, making it incompatible with Gradle 7.0.
Use '--warning-mode all' to show the individual deprecation warnings.
See https://docs.gradle.org/6.6.1/userguide/command_line_interface.html#sec:command_line_warnings

BUILD FAILED in 1h 6m 1s
852 actionable tasks: 852 executed
Build step 'Invoke Gradle script' changed build result to FAILURE
Build step 'Invoke Gradle script' marked build as failure
Archiving artifacts
Recording test results
Email was triggered for: Failure - Any
Sending email for trigger: Failure - Any
[Email-ext] Notification email body length: 446
Sending email to: builds@lucene.apache.org
Finished: FAILURE
```

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Migrated from [LUCENE-9598](https://issues.apache.org/jira/browse/LUCENE-9598) by Dawid Weiss (@dweiss), updated Nov 13 2020

Locate the Jenkins email console-log extraction patterns and compare their current output with the Gradle failure example in the issue. Improve the summary so it includes the failed task context after "FAILURE", then verify that failure emails show which task failed rather than only the build result.

Written by the indexing model from the issue text.