Revert "Temporarily disable ubuntu runners in github actions."

This reverts commit 21f934b.

Author: arobenko

.github/workflows/actions_build.yml

@@ -9,7 +9,6 @@ env:
 
 jobs:
   build_gcc_old_ubuntu_20_04:
-    if: false
     runs-on: ubuntu-20.04
     strategy:
       fail-fast: false
@@ -71,7 +70,6 @@ jobs:
         VERBOSE: 1 
 
   build_gcc_ubuntu_20_04:
-    if: false
     runs-on: ubuntu-20.04
     strategy:
       fail-fast: false
@@ -140,7 +138,6 @@ jobs:
         VERBOSE: 1 
 
   build_gcc_ubuntu_22_04:
-    if: false
     runs-on: ubuntu-22.04
     strategy:
       fail-fast: false
@@ -202,7 +199,6 @@ jobs:
         VERBOSE: 1 
 
   build_clang_old_ubuntu_20_04:
-    if: false  
     runs-on: ubuntu-20.04
     strategy:
       fail-fast: false
@@ -271,7 +267,6 @@ jobs:
         VERBOSE: 1 
 
   build_clang_ubuntu_20_04:
-    if: false  
     runs-on: ubuntu-20.04
     strategy:
       fail-fast: false
@@ -333,7 +328,6 @@ jobs:
         VERBOSE: 1 
 
   build_clang_ubuntu_22_04:
-    if: false  
     runs-on: ubuntu-22.04
     strategy:
       fail-fast: false