build: disable matrix fail-fast

Intermittent issues are causing the test matrix to fail
and whenever that happens, all other matrix options are
automatically cancelled. This increases the amount of
retries needed in order to get all tests to pass.

Signed-off-by: Paulo Gomes <paulo.gomes@weave.works>

.github/workflows/tests.yaml

@@ -64,6 +64,7 @@ jobs:
     strategy:
       matrix:
         os: [macos-10.15, macos-11, macos-12]
+      fail-fast: false
     runs-on: ${{ matrix.os }}
     steps:
       - name: Checkout