fix(ci): use macos-15 instead of deprecated macos-12 (#1048)

Author: mraszyk

.github/workflows/rust-threshold-mock-example.yml

@@ -15,7 +15,7 @@ concurrency:
   cancel-in-progress: true
 jobs:
   rust-threshold-mock-darwin:
-    runs-on: macos-12
+    runs-on: macos-15
     steps:
       - uses: actions/checkout@v1
       - name: Provision Darwin
@@ -63,4 +63,4 @@ jobs:
         run: |
           pushd rust/threshold-mock
           cargo test
-          popd
+          popd

.github/workflows/rust-x509-example.yml

@@ -16,7 +16,7 @@ concurrency:
   cancel-in-progress: true
 jobs:
   rust-x509-darwin:
-    runs-on: macos-12
+    runs-on: macos-15
     steps:
       - uses: actions/checkout@v1
       - name: Provision Darwin