Fix macos and windows CIs not running the right runners.

Author: divark

.github/workflows/macos.yml

@@ -12,7 +12,7 @@ on:
 
 jobs:
   build:
-    runs-on: ubuntu-latest
+    runs-on: macos-latest
 
     steps:
       - uses: actions/checkout@v2

.github/workflows/windows.yml

@@ -12,7 +12,7 @@ on:
 
 jobs:
   build:
-    runs-on: ubuntu-latest
+    runs-on: windows-latest
 
     steps:
       - uses: actions/checkout@v2