Downgrade ubuntu runner

Author: max-leuthaeuser

.github/workflows/pr.yml

@@ -7,7 +7,7 @@ jobs:
   test:
     strategy:
       matrix:
-        os: [ubuntu-latest, macos-latest, windows-latest]
+        os: [ubuntu-20.04, macos-latest, windows-latest]
     runs-on: ${{ matrix.os }}
     steps:
       - name: Checkout
@@ -19,7 +19,7 @@ jobs:
         with:
           swift-version: "5.9"
       - name: Run Linux Build
-        if: matrix.os == 'ubuntu-latest'
+        if: matrix.os == 'ubuntu-20.04'
         run: |
           swift build
           mv ./.build/debug/SwiftAstGen SwiftAstGen-linux

.github/workflows/release.yml

@@ -14,7 +14,7 @@ jobs:
   build:
     strategy:
       matrix:
-        os: [ubuntu-latest, macos-latest, windows-latest]
+        os: [ubuntu-20.04, macos-latest, windows-latest]
     runs-on: ${{ matrix.os }}
     steps:
       - name: Checkout
@@ -26,7 +26,7 @@ jobs:
         with:
           swift-version: "5.9"
       - name: Run Linux Build
-        if: matrix.os == 'ubuntu-latest'
+        if: matrix.os == 'ubuntu-20.04'
         run: |
           swift build -c release --arch arm64 --arch x86_64 --static-swift-stdlib
           mv ./.build/release/SwiftAstGen SwiftAstGen-linux