chore(ci): move base devel spread tests to manual

These tests are by their very nature flaky because the base devel changes
constantly and can occasionally break in a way that cannot be fixed by us.
However, we still want to keep an eye on them so repurpose the 'large'
spread run into a 'manual' one that, via cron, runs both the 'large' tests
and the 'flaky' ones.

.github/workflows/spread-large.yaml → .github/workflows/spread-manual.yaml

@@ -1,4 +1,4 @@
-name: Spread (large)
+name: Spread (manual - large/flaky)
 on:
   pull_request:
     types: [ labeled ]
@@ -7,7 +7,7 @@ on:
 
 jobs:
   snap-build:
-    if: ${{ github.event.label.name == 'run-large-spread' || github.event_name == 'schedule' }}
+    if: ${{ github.event.label.name == 'run-manual-spread' || github.event_name == 'schedule' }}
     runs-on: ubuntu-22.04
     steps:
       - name: Checkout code
@@ -24,7 +24,7 @@ jobs:
           path: ${{ steps.rockcraft.outputs.snap }}
 
   snap-tests:
-    if: ${{ github.event.label.name == 'run-large-spread' || github.event_name == 'schedule' }}
+    if: ${{ github.event.label.name == 'run-manual-spread' || github.event_name == 'schedule' }}
     runs-on: [self-hosted, spread-installed]
     needs: [snap-build]
 
@@ -43,8 +43,8 @@ jobs:
         with:
           name: snap
           path: tests
-      - name: Run spread (large)
-        run: spread tests/spread/large/
+      - name: Run spread (large/flaky)
+        run: spread tests/spread/manual/
 
       - name: Discard spread workers
         if: always()

spread.yaml

@@ -140,8 +140,8 @@ suites:
   tests/spread/foreign/:
     summary: tests that rockcraft and rocks work on different host systems
 
-  tests/spread/large/:
-    summary: bigger tests that take longer to run
+  tests/spread/manual/:
+    summary: manually-triggered tests, like bigger tests and flaky ones
     manual: true
     systems:
     - ubuntu-22.04-64