Update CI to test Swift 6.0.2 on Linux

This works around an (erroneous) compiler build error on
swift-issue-reporting.

See: pointfreeco/swift-issue-reporting#150

Author: gohanlon

.github/workflows/ci.yml

@@ -47,7 +47,7 @@ jobs:
       - name: Install Swift
         uses: swift-actions/setup-swift@v2
         with:
-          swift-version: "5.10"
+          swift-version: "6.0.2"
       - uses: actions/checkout@v4
       - name: Run tests
         run: swift test