docs/release-calendar: Shift 25.3 releases by one week

25.3.1 was planned for the day before the US Thanksgiving holiday, but
it slipped due to that holiday. The current plan puts 25.3.3 on
Christmas Eve, which will be missed for the same reason. To attempt to
fix this, I've updated the plan to move the missed release to this week,
with all releases re-aligned with that date. This moves the Christmas
Eve release to New Years Eve. We could possibly slip that by a week into
the new years as there is likely to be less work than normal done at
that time.

Due to the change in schedule I've removed one planned release, as we
should reach 25.3.Last and 26.0.1 at roughly the same time with one less
release.

Also update the last 25.2 release to match.

Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/38757>

docs/release-calendar.csv

@@ -1,11 +1,10 @@
-25.2,2025-11-26,25.2.8,Eric Engestrom,
-25.3,2025-11-26,25.3.1,Dylan Baker
-,2025-12-10,25.3.2,Dylan Baker
-,2025-12-24,25.3.3,Dylan Baker,
-,2026-01-07,25.3.4,Dylan Baker,
-,2026-01-21,25.3.5,Dylan Baker,
-,2026-02-04,25.3.6,Dylan Baker,
-,2026-02-18,25.3.7,Dylan Baker,This is the last planned release of the 25.3.x series.
+25.2,2025-12-03,25.2.8,Eric Engestrom,
+25.3,2025-12-03,25.3.1,Dylan Baker
+,2025-12-17,25.3.2,Dylan Baker
+,2025-12-31,25.3.3,Dylan Baker,
+,2026-01-14,25.3.4,Dylan Baker,
+,2026-01-28,25.3.5,Dylan Baker,
+,2026-02-11,25.3.6,Dylan Baker,Last planned 25.3 release
 26.0,2026-01-14,26.0.0-rc1,Eric Engestrom,26.0 branchpoint
 ,2026-01-21,26.0.0-rc2,Eric Engestrom,
 ,2026-01-28,26.0.0-rc3,Eric Engestrom,