fix(test): move the TSA/TSB fixture migration to V20260821

Story 24.1 merged V20260819__seed_reporting_year_open_fixtures.sql to main
(#313) and Story 24.2 took V20260820 (#318), both after this branch was cut.
This branch's V20260819__tsa_tsb_code_table_dates_and_seeds.sql therefore
claimed a version that was already taken.

Git merges the two cleanly, because they are differently NAMED files -- only
Flyway objects that both declare version 20260819, and it objects fatally:
"Found more than one migration with version 20260819" refuses to load and takes
the entire *IT suite down at boot. FlywayMigrationVersionUniquenessTest exists
to catch exactly this at PR time instead, and did.

Per db/README.md convention 1, the newer (unmerged) migration yields and the
merged ones are left alone, so this one moves to the next free slot: V20260821.
Only the version changes -- the script itself, and the two comment references
to it in Schedule10DocumentIT, are otherwise untouched.

No seed-data collision to resolve alongside it: Story 24.1 seeds mills 990/991
and Story 24.2 seeds none in the 7xx range, so the Schedule 10 block (710-716)
is unaffected. The migration now applies AFTER both, which is immaterial -- it
alters and seeds THE.TSA_NUMBER_CODE and THE.TSB_NUMBER_CODE, which neither of
the other two touches.

Verified on the merged tree: backend 1166 unit and 894 integration tests green,
frontend 188 tests green across Schedule 10 and every file this branch touches,
lint clean.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

Author: Rylan-cgi

backend/src/test/java/ca/bc/gov/nrs/ilcr/schedule10/Schedule10DocumentIT.java

@@ -357,7 +357,7 @@ void tsaAndSupplyBlockLists_areServedAndYearFiltered() throws Exception {
         .andExpect(jsonPath("$.codeLists.tsaNumbers[?(@.code == '16G')]", hasSize(0)))
         .andExpect(jsonPath("$.codeLists.supplyBlocks[?(@.code == '01')]", hasSize(0)))
         .andExpect(jsonPath("$.codeLists.supplyBlocks[?(@.code == '16')]", hasSize(0)))
-        // V20260819 seeds '90','Retired TSA' expiring 2010-12-31 stating it exists "to pin that the
+        // V20260821 seeds '90','Retired TSA' expiring 2010-12-31 stating it exists "to pin that the
         // year filter drops a code". Nothing pinned it until now: no stored 2021 page references
         // '90', so neither leg of the predicate can rescue it.
         .andExpect(jsonPath("$.codeLists.tsaNumbers[?(@.code == '90')]", hasSize(0)));
@@ -367,7 +367,7 @@ void tsaAndSupplyBlockLists_areServedAndYearFiltered() throws Exception {
   @DisplayName("an expired block a stored page references is rescued by the referenced-union leg")
   void supplyBlocks_referencedUnionRescuesAnExpiredCode() throws Exception {
     // The union leg on both queries had NO coverage: it can only rescue a code that HAS a row and
-    // fell outside the date window, and no fixture created that shape until V20260819 was corrected
+    // fell outside the date window, and no fixture created that shape until V20260821 was corrected
     // to seed '16Z' expired (see that file's CORRECTED note). Page 8904 references it, on mill 712.
     mockMvc.perform(get(ENDPOINT).param("millId", "712").param("year", "2021")
             .accept(MediaType.APPLICATION_JSON))