fix: bump deprecated macos-13 to macos-15-intel in CI (#56)

Author: mraszyk

.github/workflows/pocket-ic-server-action-test.yml

@@ -17,12 +17,12 @@ jobs:
             os: ubuntu-latest
           - version: '5.0.0'
             expected-version: '5.0.0'
-            os: macos-13 # x86_64
+            os: macos-15-intel # x86_64
 
           - expected-version: '11.0.0'
             os: ubuntu-latest
           - expected-version: '11.0.0'
-            os: macos-13 # x86_64
+            os: macos-15-intel # x86_64
           - expected-version: '11.0.0'
             os: macos-latest # arm64
 
@@ -31,7 +31,7 @@ jobs:
             os: ubuntu-latest
           - version: 'ee4c728d94b10437f41edf564650ac63cd0c0c5d'
             expected-version: '10.0.0'
-            os: macos-13 # x86_64
+            os: macos-15-intel # x86_64
           - version: 'ee4c728d94b10437f41edf564650ac63cd0c0c5d'
             expected-version: '10.0.0'
             os: macos-latest # arm64