run some jobs on the final commit only

These are too expensive to be worth running against all commits.

bin/job

@@ -49,6 +49,26 @@ commit_passed() (
     [[ -f ".gitlab-ci.d/passed/$1/$(git rev-parse HEAD)" ]]
 )
 
+contains() (
+    set -euo pipefail
+
+    local -n xs=$1
+
+    for x in "${xs[@]}"; do
+        if [[ "$x" == "$2" ]]; then
+            return 0
+        else
+            return 1
+        fi
+    done
+)
+
+# Jobs that should only run on the latest commit rather than since the branch's
+# base.
+last_commit_only=(
+    artifacts
+)
+
 run() (
     set -euo pipefail
 
@@ -67,7 +87,10 @@ run() (
 
     cd "$(git rev-parse --show-toplevel)"
 
-    if [[ -z "${CI_MERGE_REQUEST_DIFF_BASE_SHA+x}" ]]; then
+    if \
+        [[ -z "${CI_MERGE_REQUEST_DIFF_BASE_SHA+x}" ]] \
+        || contains last_commit_only "$job"
+    then
         echo "Running against latest commit only..."
 
         job_"$job" || bail