ci: replace eol mac runner with mac-12

.github/workflows/tests.yml

diff --git a/.github/workflows/tests.yml b/.github/workflows/tests.yml
index bbf450d..efa6be3 100644
--- a/.github/workflows/tests.yml
+++ b/.github/workflows/tests.yml
@@ -18,7 +18,7 @@
   build:
     strategy:
       matrix:
-        os: ['macos-10.15', 'ubuntu-latest']
+        os: ['macos-12', 'ubuntu-latest']
     runs-on: ${{ matrix.os }}
 
     steps: