CI: Use ubuntu-16.04

Author: messense

.github/workflows/CI.yml

@@ -5,7 +5,7 @@ name: CI
 jobs:
   check:
     name: Check
-    runs-on: ubuntu-latest
+    runs-on: ubuntu-16.04
     steps:
       - uses: actions/checkout@v2
       - name: Checkout submodules
@@ -30,7 +30,7 @@ jobs:
 
   test:
     name: Test Suite
-    runs-on: ubuntu-latest
+    runs-on: ubuntu-16.04
     steps:
       - uses: actions/checkout@v2
       - name: Checkout submodules
@@ -55,7 +55,7 @@ jobs:
 
   fmt:
     name: Rustfmt
-    runs-on: ubuntu-latest
+    runs-on: ubuntu-16.04
     steps:
       - uses: actions/checkout@v2
       - uses: actions-rs/toolchain@v1
@@ -67,4 +67,4 @@ jobs:
       - uses: actions-rs/cargo@v1
         with:
           command: fmt
-          args: --all -- --check
+          args: --all -- --check

.github/workflows/Release.yml

@@ -8,7 +8,7 @@ on:
 jobs:
   release:
     name: Release
-    runs-on: ubuntu-latest
+    runs-on: ubuntu-16.04
     steps:
       - uses: actions/checkout@v2
       - name: Checkout submodules