fix(e2e): resolve the Darwin fixture path on bash 3.2 (#3798)

* fix(e2e): resolve the Darwin fixture path on bash 3.2

The per-OS fixture path was built with "${fixture_metrics::-4}". A
negative substring length needs bash 4.2, and macOS still ships bash 3.2,
where the expansion fails, fixture_metrics keeps pointing at the Linux
fixture, and ./end-to-end-test.sh -u run on a Mac overwrites
collector/fixtures/e2e-output.txt with Darwin output.

"${fixture_metrics%.txt}" is equivalent and works on both.

Also strip node_thermal_temperature_celsius along with the other
non-deterministic metrics. Its sensor names and values are per-machine,
so a developer running the suite on real hardware sees the whole sensor
list as a diff. The CI runner reports no thermal sensors, so this makes
no difference there.

Signed-off-by: SaiPisey2 <piseysai0202@gmail.com>

* Apply suggestion from @SuperQ

Signed-off-by: Ben Kochie <superq@gmail.com>

---------

Signed-off-by: SaiPisey2 <piseysai0202@gmail.com>
Signed-off-by: Ben Kochie <superq@gmail.com>
Co-authored-by: Ben Kochie <superq@gmail.com>