[ci] Address @bitstreams//BUILD.bazel nullifying action cache

Place bitstreams from other jobs in a consistent location, so the
BUILD.bazel file and the command line for the action are not needlessly
changed for every CI run.

Originally, the git revision would be part of the path name to source
files, and this precluded any possibility of getting a hit to the action
cache.

Signed-off-by: Alexander Williams <[email protected]>

ci/scripts/run-fpga-tests.sh

@@ -8,9 +8,6 @@ set -e
 
 . util/build_consts.sh
 
-SHA=$(git rev-parse HEAD)
-readonly SHA
-
 if [ $# == 0 ]; then
     echo >&2 "Usage: run-fpga-tests.sh <fpga> <tags>"
     echo >&2 "E.g. ./run-fpga-tests.sh cw310 cw310_rom"
@@ -23,7 +20,7 @@ fpga_tags=("$@")
 
 # Copy bitstreams and related files into the cache directory so Bazel will have
 # the corresponding targets in the @bitstreams workspace.
-readonly BIT_CACHE_DIR="${HOME}/.cache/opentitan-bitstreams/cache/${SHA}"
+readonly BIT_CACHE_DIR="${HOME}/.cache/opentitan-bitstreams/cache/ci_bitstreams"
 if [ "${fpga}" = "hyper310" ]; then
     readonly BIT_SRC_DIR="${BIN_DIR}/hw/top_earlgrey/chip_earlgrey_cw310_hyperdebug"
 else
@@ -32,8 +29,7 @@ fi
 mkdir -p "${BIT_CACHE_DIR}"
 cp -rt "${BIT_CACHE_DIR}" "${BIT_SRC_DIR}"/*
 
-echo -n "$SHA" > "${BIT_CACHE_DIR}/../../latest.txt"
-export BITSTREAM="--offline --list ${SHA}"
+export BITSTREAM="--offline --list ci_bitstreams"
 
 # We will lose serial access when we reboot, but if tests fail we should reboot
 # in case we've crashed the UART handler on the CW310's SAM3U