ci: Default jobs to ubuntu-24.04 but allow for overrides

Author: tgross35

.github/workflows/ci.yaml

@@ -103,22 +103,18 @@ jobs:
         include:
           - target: i686-unknown-linux-gnu
             docker: true
-            os: ubuntu-24.04
           - target: i686-unknown-linux-gnu
             docker: true
-            os: ubuntu-24.04
             artifact-tag: offset-bits64
             env:
               RUST_LIBC_UNSTABLE_GNU_FILE_OFFSET_BITS: 64
           - target: i686-unknown-linux-gnu
             docker: true
-            os: ubuntu-24.04
             artifact-tag: time-bits64
             env:
               RUST_LIBC_UNSTABLE_GNU_TIME_BITS: 64
           - target: x86_64-unknown-linux-gnu
             docker: true
-            os: ubuntu-24.04
           - target: aarch64-apple-darwin
             os: macos-15
           - target: x86_64-pc-windows-gnu
@@ -135,7 +131,7 @@ jobs:
           #    ARCH: i686
           - target: i686-pc-windows-msvc
             os: windows-2025
-    runs-on: ${{ matrix.os }}
+    runs-on: ${{ matrix.os || ubuntu-24.04 }}
     timeout-minutes: 25
     env:
       TARGET: ${{ matrix.target }}
@@ -175,7 +171,6 @@ jobs:
   test_tier2:
     name: Test tier2
     needs: [test_tier1, style_check]
-    runs-on: ubuntu-24.04
     strategy:
       fail-fast: true
       max-parallel: 12
@@ -248,6 +243,7 @@ jobs:
           #   env:
           #     RUST_LIBC_UNSTABLE_GNU_TIME_BITS: 64
           #   artifact-tag: time-bits64
+    runs-on: ${{ matrix.os || ubuntu-24.04 }}
     timeout-minutes: 25
     env:
       TARGET: ${{ matrix.target }}