install missing headers on ubuntu 20.04

.github/workflows/build-ton-linux-x86-64-portable.yml

@@ -21,6 +21,12 @@ jobs:
         sudo apt-get update
         sudo apt-get install -y build-essential git cmake ninja-build libc++-dev libc++abi-dev
 
+    - if: matrix.os == 'ubuntu-20.04'
+      run: |
+        sudo apt install -y manpages-dev software-properties-common
+        sudo add-apt-repository ppa:ubuntu-toolchain-r/test
+        sudo apt update && sudo apt install gcc-11 g++-11
+
     - name: Build TON
       run: |
         git submodule sync --recursive

.github/workflows/ton-x86-64-linux.yml

@@ -1,4 +1,4 @@
-name: Ubuntu TON build (portable, x86-64)
+name: Ubuntu TON build (nixpkgs, x86-64)
 
 on: [push,workflow_dispatch,workflow_call]