jtreg retrieval for jdk25u is failing with a checksum error

Example from https://ci.adoptium.net/job/Test_openjdk25_hs_extended.openjdk_riscv64_linux/7/console (Previous job #6 has the same problem, so this seems relatively recent)
```
23:40:07 [exec] --> file downloaded to /home/jenkins/workspace/Test_openjdk25_hs_extended.openjdk_riscv64_linux/../../testDependency/lib/jtreg_7_5_1.tar.gz
23:40:07 [exec] downloading https://ci.adoptium.net/job/dependency_pipeline/lastSuccessfulBuild/artifact/jtreg/jtreg-7.5+1.tar.gz.sha256sum.txt
23:40:07 [exec] --> file downloaded to /home/jenkins/workspace/Test_openjdk25_hs_extended.openjdk_riscv64_linux/../../testDependency/lib/jtreg_7_5_1.tar.gz.sha256sum.txt
23:40:07 [exec] Expected sha is:
23:40:07 [exec] ,
23:40:07 [exec] Actual sha is : af61eaef6c3b669f076fad0456dfd2f8b0b468ea15572c5ebb05a95b9c525b7d.
23:40:07 [exec] ERROR: sha checksum error.
23:40:07 [exec] Please delete /home/jenkins/workspace/Test_openjdk25_hs_extended.openjdk_riscv64_linux/../../testDependency/lib/jtreg_7_5_1.tar.gz and rerun the program!
23:40:07
23:40:07 BUILD FAILED
```
This is potentially related to https://github.com/adoptium/ci-jenkins-pipelines/pull/1186 which was merged on Feb 23rd.

Start with the cited Test_openjdk25_hs_extended.openjdk_riscv64_linux job log and compare the jtreg retrieval behavior with ci-jenkins-pipelines PR 1186. Trace how the jtreg archive and .sha256sum.txt file are obtained; done means the expected SHA is populated and the affected jdk25u job passes checksum validation.

Written by the indexing model from the issue text.