[ci] Vivado log display step is broken

Nobody has claimed this yet.

### Description

Currently the "Display synthesis & implementation logs" step of the bitstream build job in CI always fails to show any of the synthesis/implementation logs or the utilization & timing summary report. See for example:
https://github.com/lowRISC/opentitan/actions/runs/18542321956/job/52852819628#step:7:23

> cat: /home/runner/_work/opentitan/opentitan/build-out/hw/top_earlgrey/chip_earlgrey_cw310_hyperdebug/build.fpga_cw310_hyperdebug/lowrisc_systems_chip_earlgrey_cw310_hyperdebug_0.1/synth-vivado/lowrisc_systems_chip_earlgrey_cw310_hyperdebug_0.1.runs/synth_1/runme.log: No such file or directory
Implementation log
cat: /home/runner/_work/opentitan/opentitan/build-out/hw/top_earlgrey/chip_earlgrey_cw310_hyperdebug/build.fpga_cw310_hyperdebug/lowrisc_systems_chip_earlgrey_cw310_hyperdebug_0.1/synth-vivado/lowrisc_systems_chip_earlgrey_cw310_hyperdebug_0.1.runs/impl_1/runme.log: No such file or directory
Utilization report
cat: /home/runner/_work/opentitan/opentitan/build-out/hw/top_earlgrey/chip_earlgrey_cw310_hyperdebug/build.fpga_cw310_hyperdebug/lowrisc_systems_chip_earlgrey_cw310_hyperdebug_0.1/synth-vivado/lowrisc_systems_chip_earlgrey_cw310_hyperdebug_0.1.runs/impl_1/chip_earlgrey_cw310_hyperdebug_utilization_placed.rpt: No such file or directory
Timing summary report
cat: /home/runner/_work/opentitan/opentitan/build-out/hw/top_earlgrey/chip_earlgrey_cw310_hyperdebug/build.fpga_cw310_hyperdebug/lowrisc_systems_chip_earlgrey_cw310_hyperdebug_0.1/synth-vivado/lowrisc_systems_chip_earlgrey_cw310_hyperdebug_0.1.runs/impl_1/chip_earlgrey_cw310_hyperdebug_timing_summary_routed.rpt: No such file or directory

This is somewhat related to https://github.com/lowRISC/opentitan/issues/28109 (and would probably be useful for that).

Start with the linked GitHub Actions bitstream build job and inspect the “Display synthesis & implementation logs” step, including the paths used for the synthesis and implementation logs and reports. Reproduce or inspect a failing run, then verify that the step displays both logs and the utilization and timing summary reports without missing-file errors.

Written by the indexing model from the issue text.