use ubuntu-16.04 runner

Author: swannodette

.github/workflows/test.yaml

@@ -5,7 +5,7 @@ jobs:
   # Runtime Tests
   runtime-test:
     name: Runtime Tests
-    runs-on: ubuntu-latest
+    runs-on: ubuntu-16.04
     steps:
       - uses: actions/checkout@v2
 
@@ -57,7 +57,7 @@ jobs:
   # Self-host Tests
   self-host-test:
     name: Self-host Tests
-    runs-on: ubuntu-latest
+    runs-on: ubuntu-16.04
     steps:
       - uses: actions/checkout@v2
 
@@ -96,7 +96,7 @@ jobs:
   # Self-parity Tests
   self-parity-test:
     name: Self-parity Tests
-    runs-on: ubuntu-latest
+    runs-on: ubuntu-16.04
     steps:
       - uses: actions/checkout@v2
 
@@ -135,7 +135,7 @@ jobs:
   # Compiler Tests
   compiler-test:
     name: Compiler Tests
-    runs-on: ubuntu-latest
+    runs-on: ubuntu-16.04
     steps:
       - uses: actions/checkout@v2
 
@@ -169,7 +169,7 @@ jobs:
   # CLI Tests
   cli-test:
     name: CLI Tests
-    runs-on: ubuntu-latest
+    runs-on: ubuntu-16.04
     steps:
       - uses: actions/checkout@v2
         with: