.github/workflows: use ubuntu-slim on simple actions

Use GitHub's new slim runners with 1 vCPU for simple actions that
don't need more CPUs or RAM.

Note: the ubuntu-slim image doesn't have Java or Maven so we can't
run any actions that use those (for example codescan).

See: https://github.blog/changelog/2026-01-22-1-vcpu-linux-runner-now-generally-available-in-github-actions/

Author: alanorth

.github/workflows/issue_opened.yml

@@ -8,7 +8,7 @@ on:
 permissions: {}
 jobs:
   automation:
-    runs-on: ubuntu-latest
+    runs-on: ubuntu-slim
     steps:
     # Add the new issue to a project board, if it needs triage
     # See https://github.com/actions/add-to-project

.github/workflows/label_merge_conflicts.yml

@@ -18,7 +18,7 @@ jobs:
   triage:
     # Ensure this job never runs on forked repos. It's only executed for 'dspace/dspace'
     if: github.repository == 'dspace/dspace'
-    runs-on: ubuntu-latest
+    runs-on: ubuntu-slim
     permissions:
       pull-requests: write
     steps:

.github/workflows/port_merged_pull_request.yml

@@ -18,7 +18,7 @@ permissions:
 
 jobs:
   port_pr:
-    runs-on: ubuntu-latest
+    runs-on: ubuntu-slim
     # Don't run on closed *unmerged* pull requests
     if: github.event.pull_request.merged
     steps:
@@ -43,4 +43,4 @@ jobs:
           merge_commits: 'skip'
           # Use a personal access token (PAT) to create PR as 'dspace-bot' user.
           # A PAT is required in order for the new PR to trigger its own actions (for CI checks)
-          github_token: ${{ secrets.PR_PORT_TOKEN }}
+          github_token: ${{ secrets.PR_PORT_TOKEN }}

.github/workflows/pull_request_opened.yml

@@ -16,7 +16,7 @@ permissions:
 
 jobs:
   automation:
-    runs-on: ubuntu-latest
+    runs-on: ubuntu-slim
     steps:
     # Assign the PR to whomever created it. This is useful for visualizing assignments on project boards
     # See https://github.com/toshimaru/auto-author-assign

.github/workflows/stale.yml

@@ -12,7 +12,7 @@ permissions:
 
 jobs:
   stale:
-    runs-on: ubuntu-latest
+    runs-on: ubuntu-slim
     steps:
       - uses: actions/stale@v10
         with: