Failed proptest on CI: linalg::eigen::proptest_tests::f64::symmetric_eigen_static_square_3x3

```
---- linalg::eigen::proptest_tests::f64::symmetric_eigen_static_square_3x3 stdout ----
proptest: Saving this and future failures in /home/runner/work/nalgebra/nalgebra/proptest-regressions/linalg/eigen.txt
proptest: If this test was run on a CI system, you may wish to add the following line to your copy of the file. (You may need to create it.)
cc 4506e04bfcb6ef187e64e082f2721c6db066957302200a70de240df35bd21965
thread 'linalg::eigen::proptest_tests::f64::symmetric_eigen_static_square_3x3' panicked at 'Test failed: assertion failed: relative_eq!(m.lower_triangle(), recomp.lower_triangle(), epsilon = 1.0e-5) at tests/linalg/eigen.rs:71.
minimal failing input: m = [
[
-9.06080145695772,
-56.79017019665934,
-49.70088416407505,
],
[
-91.76150602349615,
-90.35786435657262,
2.631286114890164,
],
[
96.16903275852768,
75.75772[783](https://github.com/dimforge/nalgebra/actions/runs/5851690899/job/15862830704?pr=1273#step:3:784)044047,
22.64631009656657,
],
]
successes: 144
local rejects: 0
global rejects: 0
', tests/linalg/eigen.rs:71:5
```

Start with tests/linalg/eigen.rs at line 71 and the failing symmetric_eigen_static_square_3x3 proptest. Reproduce it using the minimal matrix shown and inspect proptest-regressions/linalg/eigen.txt, including the recorded case. Done means the regression no longer fails at the reported relative_eq! assertion and the eigen decomposition remains covered by the test.

Written by the indexing model from the issue text.