github: remove operative system from continuous matrix

Author: mcraveiro

.github/workflows/continuous-linux.yml

@@ -13,7 +13,7 @@ on:
 jobs:
   build:
     name: ${{matrix.family}}-${{matrix.compiler}}-${{matrix.buildtype}}
-    runs-on: ${{matrix.os}}-latest
+    runs-on: ubuntu-latest
     environment: CI
     strategy:
       fail-fast: false
@@ -23,11 +23,9 @@ jobs:
         include:
           - name: linux-gcc
             family: linux
-            os: ubuntu
             compiler: gcc
           - name: linux-clang
             family: linux
-            os: ubuntu
             compiler: clang
     steps:
       - uses: actions/checkout@v2

.github/workflows/continuous-macos.yml

@@ -13,7 +13,7 @@ on:
 jobs:
   build:
     name: ${{matrix.family}}-${{matrix.compiler}}-${{matrix.buildtype}}
-    runs-on: ${{matrix.os}}-latest
+    runs-on: macos-latest
     environment: CI
     strategy:
       fail-fast: false
@@ -23,7 +23,6 @@ jobs:
         include:
           - name: macos-clang
             family: macos
-            os: macos
             compiler: clang
     steps:
       - uses: actions/checkout@v2

.github/workflows/continuous-windows.yml

@@ -13,7 +13,7 @@ on:
 jobs:
   windows:
     name: ${{matrix.family}}-${{matrix.compiler}}-${{matrix.buildtype}}
-    runs-on: ${{matrix.os}}-latest
+    runs-on: windows-latest
     environment: CI
     strategy:
       fail-fast: false
@@ -22,15 +22,8 @@ jobs:
         buildtype: [debug, release]
         include:
           - name: windows-msvc
-            os: windows
             family: windows
             compiler: msvc
-          # FIXME: can't use this until allow_failures is added to github.
-          # See https://github.com/actions/toolkit/issues/399
-          # - name: windows-msvc-clang-cl
-          #   os: windows
-          #   family: windows
-          #   compiler: msvc-clang-cl
     steps:
       - uses: actions/checkout@v2
         with: