Revert "ci: bump ubuntu runner from 20.04 to 24.04"

This reverts commit c95399c.

Author: DennisDyallo

.github/workflows/build-nativeshims.yml

@@ -64,7 +64,7 @@ jobs:
 
   build-linux-amd64:
     name: Build Linux (amd64)
-    runs-on: ubuntu-24.04
+    runs-on: ubuntu-20.04
     steps:
       - uses: actions/checkout@v4
       - run: |
@@ -78,7 +78,7 @@ jobs:
 
   build-linux-arm64:
     name: Build Linux (arm64)
-    runs-on: ubuntu-24.04
+    runs-on: ubuntu-20.04
     steps:
       - uses: actions/checkout@v4
       - run: |

Yubico.NativeShims/build-linux-amd64.sh

@@ -24,7 +24,7 @@ DEBIAN_FRONTEND=noninteractive sudo apt-get install -yq \
     g++ \
     gcc
 
-# Install latest version of CMake for Ubuntu
+# Install latest version of CMake for Ubuntu 20.04
 wget -O - https://apt.kitware.com/keys/kitware-archive-latest.asc 2>/dev/null | gpg --dearmor - | sudo tee /usr/share/keyrings/kitware-archive-keyring.gpg >/dev/null
 echo 'deb [signed-by=/usr/share/keyrings/kitware-archive-keyring.gpg] https://apt.kitware.com/ubuntu/ focal main' | sudo tee /etc/apt/sources.list.d/kitware.list >/dev/null
 sudo apt-get update -qq

Yubico.NativeShims/build-linux-arm64.sh

@@ -25,7 +25,7 @@ DEBIAN_FRONTEND=noninteractive sudo apt-get install -yq \
     g++-aarch64-linux-gnu \
     gcc-aarch64-linux-gnu \
 
-# Install latest version of CMake for Ubuntu
+# Install latest version of CMake for Ubuntu 20.04
 wget -O - https://apt.kitware.com/keys/kitware-archive-latest.asc 2>/dev/null | gpg --dearmor - | sudo tee /usr/share/keyrings/kitware-archive-keyring.gpg >/dev/null
 echo 'deb [signed-by=/usr/share/keyrings/kitware-archive-keyring.gpg] https://apt.kitware.com/ubuntu/ focal main' | sudo tee /etc/apt/sources.list.d/kitware.list >/dev/null
 sudo apt-get update -qq