ci: fix e2e_benchmark comparison

[m1ghtym0]

Context

The e2e_benchmark test correctly compares the current benchmark with the previous one.
However, there are two problems:

1. The comparison results do not lead to a failed test due to wrong/missing error handling
2. The test ALWAYS overwrites the stored results in the S3 bucket with the new results, leading to a degradation of our baseline

Proposed change(s)

• Update comparison to fail when the new values are outside the threshold (80% of the previous benchmark)
• Only upload new results if the comparison succeeds -> Baseline can still slowly degrade, but I'd suspect the performance to either be stable or drop significantly in a single step

Additional info

• https://github.com/edgelesssys/constellation/actions/runs/7637200058
• Keeping a longer history of results is out of scope for this PR
• We could introduce fixed baseline values if we want to

Checklist

• Add labels (e.g., for changelog category)
• Is PR title adequate for changelog?

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[m1ghtym0]

Test with failure case failed correctly: https://github.com/edgelesssys/constellation/actions/runs/7652366550