Switch to the new GitHub Actions runner groups (#303)

To update to Ubuntu 24.04, and to prevent the rate limit issues
mentioned here:
heroku/buildpacks-go#283

I've not added the run image pre-pulling step used by some of
the other CNB repos, since this repo doesn't currently use a matrix
to test builder image versions, and instead varies the builder test
by test, which (a) means I'd have to hardcode a list, (b) means that
the benefit is less.

See also:
https://salesforce.quip.com/bu6UA0KImOxJ#temp:C:GZR57becb9df8d94f80b132168fd
https://github.com/actions/runner-images/blob/main/images/ubuntu/Ubuntu2404-Readme.md

GUS-W-16238120.

.github/workflows/check_changelog.yml

@@ -9,7 +9,7 @@ permissions:
 
 jobs:
   check-changelog:
-    runs-on: ubuntu-latest
+    runs-on: ubuntu-24.04
     if: (!contains(github.event.pull_request.labels.*.name, 'skip changelog'))
     steps:
       - name: Checkout

.github/workflows/ci.yml

@@ -15,7 +15,7 @@ env:
 
 jobs:
   lint:
-    runs-on: ubuntu-22.04
+    runs-on: ubuntu-24.04
     steps:
       - name: Checkout
         uses: actions/checkout@v4
@@ -29,7 +29,7 @@ jobs:
         run: cargo fmt -- --check
 
   unit-test:
-    runs-on: ubuntu-22.04
+    runs-on: ubuntu-24.04
     steps:
       - name: Checkout
         uses: actions/checkout@v4
@@ -41,7 +41,7 @@ jobs:
         run: cargo test --locked
 
   integration-test:
-    runs-on: ubuntu-22.04
+    runs-on: ubuntu-24.04
     steps:
       - name: Checkout
         uses: actions/checkout@v4
@@ -60,7 +60,7 @@ jobs:
         run: cargo test --locked -- --ignored
 
   print-pack-getting-started-output:
-    runs-on: ${{ matrix.target == 'aarch64-unknown-linux-musl' && 'pub-hk-ubuntu-22.04-arm-medium' || 'ubuntu-latest' }}
+    runs-on: ${{ matrix.target == 'aarch64-unknown-linux-musl' && 'pub-hk-ubuntu-24.04-arm-medium' || 'ubuntu-24.04' }}
     strategy:
       matrix:
         target: ["aarch64-unknown-linux-musl", "x86_64-unknown-linux-musl"]
@@ -97,7 +97,7 @@ jobs:
         run: pack build my-image --force-color --builder heroku/builder:24 --buildpack heroku/nodejs-engine --buildpack packaged/${{ matrix.target }}/debug/heroku_ruby --path tmp/ruby-getting-started --pull-policy never
 
   print-style-guide:
-    runs-on: ubuntu-22.04
+    runs-on: ubuntu-24.04
     steps:
       - name: Checkout
         uses: actions/checkout@v4