Switch from ubuntu-latest to ubuntu-20.04

To address two problems:
1. Make CICD stable and independent from OS updates
2. Fix problem with `actions/setup-python` and `actions/setup-java` not
   working on `ubuntu-latest`

Author: dkropachev

.github/workflows/build-pre-release.yml

@@ -20,7 +20,7 @@ jobs:
       fail-fast: false
       matrix:
         include:
-          - os: ubuntu-latest
+          - os: ubuntu-20.04
             platform: x86_64
     steps:
       - uses: actions/checkout@v4

.github/workflows/build-push.yml

@@ -25,10 +25,10 @@ jobs:
       fail-fast: false
       matrix:
         include:
-          - os: ubuntu-latest
+          - os: ubuntu-20.04
             platform: x86_64
 
-          - os: ubuntu-latest
+          - os: ubuntu-20.04
             platform: PyPy
 
           - os: windows-latest
@@ -128,7 +128,7 @@ jobs:
   build_sdist:
     name: Build source distribution
     if: "(!contains(github.event.pull_request.labels.*.name, 'disable-test-build'))|| github.event_name == 'push' && endsWith(github.event.ref, 'scylla')"
-    runs-on: ubuntu-latest
+    runs-on: ubuntu-20.04
     steps:
       - uses: actions/checkout@v4
 
@@ -148,7 +148,7 @@ jobs:
   build_wheels_extra_arch:
     if: "(!contains(github.event.pull_request.labels.*.name, 'disable-test-build'))|| github.event_name == 'push' && endsWith(github.event.ref, 'scylla')"
     # The host should always be linux
-    runs-on: ubuntu-latest
+    runs-on: ubuntu-20.04
     name: Build extra arch ${{ matrix.archs }} wheels
     strategy:
       fail-fast: false
@@ -185,7 +185,7 @@ jobs:
 
   upload_pypi:
     needs: [build_wheels, build_wheels_extra_arch, build_sdist]
-    runs-on: ubuntu-latest
+    runs-on: ubuntu-20.04
     permissions:
       id-token: write
 

.github/workflows/docs-pages.yaml

@@ -13,7 +13,7 @@ on:
 
 jobs:
   release:
-    runs-on: ubuntu-latest
+    runs-on: ubuntu-20.04
     steps:
       - name: Checkout
         uses: actions/checkout@v4

.github/workflows/docs-pr.yaml

@@ -11,7 +11,7 @@ on:
 
 jobs:
   build:
-    runs-on: ubuntu-latest
+    runs-on: ubuntu-20.04
     steps:
       - name: Checkout
         uses: actions/checkout@v4

.github/workflows/integration-tests.yml

@@ -12,7 +12,7 @@ jobs:
   tests:
     name: test ${{ matrix.event_loop_manager }} (${{ matrix.python-version }})
     if: "!contains(github.event.pull_request.labels.*.name, 'disable-integration-tests')"
-    runs-on: ubuntu-latest
+    runs-on: ubuntu-20.04
     strategy:
       fail-fast: false
       matrix: