chore: updated semgrep error outputs to include stdout and stderr

[art1f1c3R]

Summary

This is a quick PR that just includes the standard output and error of Semgrep when it fails to run.

Description of changes

This PR includes Semgrep stderr and stdout, which makes it easier to determine what caused Semgrep to fail, e.g.:

│ [INFO] 06:36:37 2026-04-23 06:36:37,891  Unable to run semgrep scan --metrics off --disable-version-check --oss-only --disable-nosem --config                                                                                     │
│ /scratch/cflottma/python-malware-dev/macaron/src/macaron/resources/pypi_malware_rules /tmp/Django-5.0.6_qvu0216_/Django-5.0.6 --json-output=/tmp/tmpusseunzu on /tmp/Django-5.0.6_qvu0216_/Django-5.0.6: Command '['semgrep',     │
│ 'scan', '--metrics', 'off', '--disable-version-check', '--oss-only', '--disable-nosem', '--config', '/scratch/cflottma/python-malware-dev/macaron/src/macaron/resources/pypi_malware_rules',                                      │
│ '/tmp/Django-5.0.6_qvu0216_/Django-5.0.6', '--json-output=/tmp/tmpusseunzu']' returned non-zero exit status 2.                                                                                                                    │
│                 Return code: 2                                                                                                                                                                                                    │
│                 stdout:                                                                                                                                                                                                           │
│                 stderr: Failed to find semgrep-core in PATH or in the semgrep package.

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