github: Add macos-26 to the test matrix

Author: bep

.github/workflows/test.yml

@@ -17,7 +17,7 @@ jobs:
     strategy:
       matrix:
         go-version: [1.24.x, 1.25.x]
-        os: [ubuntu-latest, windows-latest] # macos disabled for now because of disk space issues.
+        os: [ubuntu-latest, windows-latest, macos-26]
     runs-on: ${{ matrix.os }}
     steps:
       - if: matrix.os == 'ubuntu-latest'