GitHub Actions: bump runners ubuntu version to latest available

Accoring to [1] Ubuntu 20.04 runners in GitHub will be fully unsuppoerted
by 2025-04-01. This commit bumps GitHub-provided runners to latest available
Ubuntu 24.04

I am not changing runners to latest because fixed version guarantees
stability of packages across workflow runs

[1] - actions/runner-images#11101

Signed-off-by: Pavel Abramov <uncle.decart@gmail.com>

.github/workflows/ci.yaml

@@ -9,7 +9,7 @@ on:
 
 jobs:
   build:
-    runs-on: ubuntu-20.04
+    runs-on: ubuntu-24.04
     steps:
       - name: Checkout
         uses: actions/checkout@v2

.github/workflows/publish.yaml

@@ -14,7 +14,7 @@ env:
 
 jobs:
   publish:
-    runs-on: ubuntu-20.04
+    runs-on: ubuntu-24.04
     steps:
       - name: Checkout
         uses: actions/checkout@v2

.github/workflows/release.yaml

@@ -11,7 +11,7 @@ env:
 
 jobs:
   release:
-    runs-on: ubuntu-20.04
+    runs-on: ubuntu-24.04
     permissions:
       packages: write
       contents: read