Update dependency ubuntu to v26

.github/workflows/backport.yml

@@ -18,7 +18,7 @@ jobs:
   # The main gotchas with this action are that it _only_ supports merge commits,
   # and that PRs _must_ be labelled before they're merged to trigger a backport.
   open-pr:
-    runs-on: ubuntu-24.04
+    runs-on: ubuntu-26.04
     if: github.event.pull_request.merged
     steps:
       - name: Checkout

.github/workflows/ci.yml

@@ -15,7 +15,7 @@ env:
 
 jobs:
   check-diff:
-    runs-on: ubuntu-24.04
+    runs-on: ubuntu-26.04
 
     steps:
       - name: Checkout
@@ -35,7 +35,7 @@ jobs:
         run: make check-diff
 
   detect-noop:
-    runs-on: ubuntu-24.04
+    runs-on: ubuntu-26.04
     outputs:
       noop: ${{ steps.noop.outputs.should_skip }}
     steps:
@@ -49,7 +49,7 @@ jobs:
           concurrent_skipping: false
 
   lint:
-    runs-on: ubuntu-24.04
+    runs-on: ubuntu-26.04
     needs: detect-noop
     if: needs.detect-noop.outputs.noop != 'true'
 
@@ -76,7 +76,7 @@ jobs:
           version: ${{ env.GOLANGCI_VERSION }}
 
   codeql:
-    runs-on: ubuntu-24.04
+    runs-on: ubuntu-26.04
     needs: detect-noop
     if: needs.detect-noop.outputs.noop != 'true'
 
@@ -103,7 +103,7 @@ jobs:
         uses: github/codeql-action/analyze@1c5b675653bb5c22dbe9b12b556ec555138e09fd # v4
 
   unit-tests:
-    runs-on: ubuntu-24.04
+    runs-on: ubuntu-26.04
     needs: detect-noop
     if: needs.detect-noop.outputs.noop != 'true'
 

.github/workflows/commands.yml

@@ -4,7 +4,7 @@ on: issue_comment
 
 jobs:
   points:
-    runs-on: ubuntu-24.04
+    runs-on: ubuntu-26.04
     if: startsWith(github.event.comment.body, '/points')
 
     steps:
@@ -65,7 +65,7 @@ jobs:
   # NOTE(negz): See also backport.yml, which is the variant that triggers on PR
   # merge rather than on comment.
   backport:
-    runs-on: ubuntu-24.04
+    runs-on: ubuntu-26.04
     if: github.event.issue.pull_request && startsWith(github.event.comment.body, '/backport')
     steps:
     - name: Extract Command

.github/workflows/promote.yml

@@ -20,7 +20,7 @@ env:
 
 jobs:
   promote-artifacts:
-    runs-on: ubuntu-24.04
+    runs-on: ubuntu-26.04
 
     steps:
       - name: Checkout

.github/workflows/tag.yml

@@ -12,7 +12,7 @@ on:
 
 jobs:
   create-tag:
-    runs-on: ubuntu-24.04
+    runs-on: ubuntu-26.04
 
     steps:
       - name: Checkout