workflows/periodic-merge: set custom name for haskell-updates merge

The simple name can lead to confusion. Adding an explicit override to
make it more clear.

.github/workflows/periodic-merge-24h.yml

@@ -35,10 +35,12 @@ jobs:
             into: staging-next-25.05
           - from: staging-next-25.05
             into: staging-25.05
-          - from: master staging
+          - name: merge-base(master,staging) → haskell-updates
+            from: master staging
             into: haskell-updates
     uses: ./.github/workflows/periodic-merge.yml
     with:
       from: ${{ matrix.pairs.from }}
       into: ${{ matrix.pairs.into }}
+    name: ${{ matrix.pairs.name || format('{0} → {1}', matrix.pairs.from, matrix.pairs.into) }}
     secrets: inherit

.github/workflows/periodic-merge-6h.yml

@@ -35,4 +35,5 @@ jobs:
     with:
       from: ${{ matrix.pairs.from }}
       into: ${{ matrix.pairs.into }}
+    name: ${{ format('{0} → {1}', matrix.pairs.from, matrix.pairs.into) }}
     secrets: inherit

.github/workflows/periodic-merge.yml

@@ -15,7 +15,6 @@ on:
 jobs:
   merge:
     runs-on: ubuntu-24.04-arm
-    name: ${{ inputs.from }} → ${{ inputs.into }}
     steps:
       # Use a GitHub App to create the PR so that CI gets triggered
       # The App is scoped to Repository > Contents and Pull Requests: write for Nixpkgs