[GitHub Actions] Limit executing codecov to when Xcode is 10.3

.github/workflows/xcodebuild.yml

@@ -63,5 +63,6 @@ jobs:
           DEVELOPER_DIR: /Applications/Xcode_${{ matrix.xcode.version }}.app
         run: xcodebuild -scheme Base32 build -sdk watchsimulator | xcpretty
         shell: bash
-      - run: curl -s https://codecov.io/bash | bash -s -- -t ${{ secrets.CODECOV_TOKEN }}
+      - if: matrix.xcode.version == '10.3'
+        run: curl -s https://codecov.io/bash | bash -s -- -t ${{ secrets.CODECOV_TOKEN }}
         shell: bash