Revert "Try not caching journey test dependencies"

This reverts commit bf2abdb, the
supporting change in #1725 that refrained from caching build
artifacts from the `test-journey` job, since that no longer needs
to be avoided now that `git-daemon` journey tests aren't run on CI.

In 9566488 (#1634), journey tests that use `git-daemon` were
disabled on CI. #1725 tried reenabling them (65788e8) and fixing
them by no longer caching build artifacts with the `rust-cache`
action in the `test-journey` job (bf2abdb). This worked at the
time, but the exact reason it worked or how reliable it would be
were unknown. It stopped working shortly thereafter in 25b8480
(#1726), and those journey tests were re-disabled on CI in d1d3f7c,
which reverted 65788e8. However, bf2abdb was not reverted at that
time.

(The change in d1d3f7c from #1726, taken together with this
commit, effectively constitute a revert of PR #1725.)

Author: EliahKagan

.github/workflows/ci.yml

@@ -123,6 +123,7 @@ jobs:
     steps:
       - uses: actions/checkout@v4
       - uses: dtolnay/rust-toolchain@stable
+      - uses: Swatinem/rust-cache@v2
       - uses: extractions/setup-just@v2
       - name: Run journey tests
         run: just ci-journey-tests