Solely use ubuntu-latest for ci

Drop Windows and macOS from CI due to their long build times. Windows
and macOS are still first class platforms for gfold, but running
individual tests and builds for them in CI has not been valuable
recently.

Signed-off-by: Nick Gerace <[email protected]>

Author: nickgerace

.github/workflows/ci.yml

@@ -15,8 +15,8 @@ concurrency:
   group: "${{ github.workflow }}-${{ github.ref }}"
   cancel-in-progress: true
 jobs:
-  test:
-    name: "Lint / Test / Build (ubuntu-latest)"
+  ci:
+    name: "CI"
     runs-on: ubuntu-latest
     steps:
       - uses: actions/checkout@v2
@@ -30,25 +30,4 @@ jobs:
       - uses: actions-rs/cargo@v1
         with:
           command: xtask
-          args: ci
-  build:
-    name: "Test / Build"
-    runs-on: ${{ matrix.os }}
-    strategy:
-      matrix:
-        os: [windows-latest, macos-latest]
-    steps:
-      - uses: actions/checkout@v2
-      - uses: actions-rs/toolchain@v1
-        with:
-          profile: minimal
-          toolchain: stable
-          override: true
-      - uses: Swatinem/rust-cache@v1
-      - uses: actions-rs/cargo@v1
-        with:
-          command: test
-      - uses: actions-rs/cargo@v1
-        with:
-          command: build
-          args: --all-targets --locked
+          args: ci