Update release action to latest Ubuntu

Author: aramperes

.github/workflows/release.yml

@@ -78,7 +78,7 @@ jobs:
         build: [ linux-amd64, macos-intel, windows ]
         include:
           - build: linux-amd64
-            os: ubuntu-18.04
+            os: ubuntu-latest
             rust: stable
             target: x86_64-unknown-linux-musl
           - build: macos-intel
@@ -97,7 +97,7 @@ jobs:
           fetch-depth: 1
 
       - name: Install packages (Ubuntu)
-        if: matrix.os == 'ubuntu-18.04'
+        if: matrix.os == 'ubuntu-latest'
         run: |
           .github/ci/ubuntu-install-packages
       - name: Install packages (macOS)