Give the test job its own scoped target/ cache

test's own compiled objects are worth reusing across runs — it's the
only job needing full codegen, so it can't share anything with the
clippy jobs' check-only builds regardless of key. Scoping it to a key
the clippy jobs don't touch avoids the contention/collision problem
that came from all 5 jobs previously sharing one target/ cache key,
and since it excludes feedsignal-web, its target/ stays much smaller
than the combined cache removed earlier.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

.forgejo/workflows/ci.yml

@@ -144,6 +144,20 @@ jobs:
           restore-keys: |
             cargo-${{ runner.os }}-
 
+      # Own key, not shared with the clippy jobs above: this job is the
+      # only one that needs full codegen (clippy's check-only builds
+      # produce metadata, not the linkable artifacts `cargo test` needs,
+      # so there's nothing to share either way), and it never touches
+      # feedsignal-web, so its target/ stays far smaller than a build
+      # covering every crate's feature set.
+      - name: Cache test target directory
+        uses: actions/cache@v4
+        with:
+          path: target
+          key: target-test-${{ runner.os }}-${{ hashFiles('**/Cargo.lock') }}
+          restore-keys: |
+            target-test-${{ runner.os }}-
+
       - name: Cache sccache compilation objects
         uses: actions/cache@v4
         with: