Issue #326: update the runs-on in actions to use 20.04

Author: dalehenrich

.github/workflows/ci-Client.yml

@@ -10,7 +10,7 @@ on:
 
 jobs:
   build:
-    runs-on: ubuntu-18.04
+    runs-on: ubuntu-20.04
     strategy:
       fail-fast: false
       matrix:

.github/workflows/ci-Seaside3.yml

@@ -10,7 +10,7 @@ on:
 
 jobs:
   build:
-    runs-on: ubuntu-18.04
+    runs-on: ubuntu-20.04
     strategy:
       fail-fast: false
       matrix:

.github/workflows/ci-SmalltalkCI.yml

@@ -10,7 +10,7 @@ on:
 
 jobs:
   build:
-    runs-on: ubuntu-18.04
+    runs-on: ubuntu-20.04
     strategy:
       fail-fast: false
       matrix:

.github/workflows/ci-UnitTest.yml

@@ -10,7 +10,7 @@ on:
 
 jobs:
   build:
-    runs-on: ubuntu-18.04
+    runs-on: ubuntu-20.04
     strategy:
       fail-fast: false
       matrix:

.github/workflows/ci-UpgradeTests.yml

@@ -10,7 +10,7 @@ on:
 
 jobs:
   build:
-    runs-on: ubuntu-18.04
+    runs-on: ubuntu-20.04
     strategy:
       fail-fast: false
       matrix: