Time-zone-dependent tests are skipped or vacuous on the UTC CI runner #119

Two tests check that no time-zone rule is consulted for a wall clock the machine's zone skips or repeats, and neither can do so on the CI runner. .github/workflows/dotnet.yml runs on ubuntu-latest, whose zone is UTC, and sets no TZ. Measured on main (7f4dc47):

TZ=UTC dotnet test test/CodoMetis.ValueRanges.EFCore.PostgreSQL.Tests --filter WrapperTimestampSet_LocalElement_KeepsAWallClockTheZoneSkips
   → skipped (Assert.Inconclusive: "UTC skips no wall clock in 2026.")
TZ=UTC dotnet test test/CodoMetis.ValueRanges.Tests --filter LocalValue_RoundTrips_WithItsKind
   → passed, but 2026-03-29 02:30 and 2026-10-25 02:30 are ordinary wall clocks in UTC, so the DST rows test nothing zone-specific

• test/CodoMetis.ValueRanges.EFCore.PostgreSQL.Tests/SqlLiteralTests.cs — WrapperTimestampSet_LocalElement_KeepsAWallClockTheZoneSkips searches TimeZoneInfo.Local for an invalid time and goes Inconclusive when there is none.
• test/CodoMetis.ValueRanges.Tests/TemporalLiteralGrammarTests.cs — LocalValue_RoundTrips_WithItsKind hard-codes Europe/Berlin transition instants.

So the promise in docs/serialization.md that a local value round-trips "with its kind" through a skipped or repeated wall clock is checked only on a developer machine in a DST zone. The workflow's own comment ("nothing in the four shipping packages reads the environment … no TimeZoneInfo") is true of src/, but the tests of the local-kind rule depend on the zone by construction, and under UTC they are vacuous.

Fix: run the unit job with TZ=Europe/Berlin (or add a second matrix leg), and turn the Inconclusive into a failure when the zone has no gap, so the test can't go quiet again. Alternatively construct the skipped wall clock with TimeZoneInfo.FindSystemTimeZoneById("Europe/Berlin") and DateTime.SpecifyKind instead of relying on Local.

Found in the 10.0.0 bug hunt (code-analyst reading, reproduced here). Tests only.