Fix migrate() to update schemaVersion for all migrations, not just pre-0.6.0

[Copilot]

The migrate() function only updated schemaVersion when migrating from versions below 0.6.0, leaving it unchanged for migrations between 0.6.0+ versions (e.g., 0.6.4 → 0.7.0).

Changes

• dandischema/metadata.py: Moved schemaVersion assignment outside the pre-0.6.0 conditional block so it executes for all migrations
• dandischema/tests/test_metadata.py: Added regression test covering 0.6.0+ → current version migrations

Example

# Before: schemaVersion incorrectly remained 0.6.0
obj = {"schemaKey": "Dandiset", "schemaVersion": "0.6.0", "identifier": "DANDI:000000"}
result = migrate(obj, to_version="0.7.0")
# result["schemaVersion"] == "0.6.0"  ❌

# After: schemaVersion correctly updated to 0.7.0
# result["schemaVersion"] == "0.7.0"  ✅

• Fixes bug: migrate would assign target version only for records with schema starting versions under 0.6.0 #353

Original prompt

---

This section details on the original issue you should resolve

<issue_title>bug: migrate would assign target version only for records with schema starting versions under 0.6.0</issue_title>
<issue_description>I didn't validate that issue exists, so first the issue should be demonstrated in our existing tests -- may be I am not reviewing code correctly. But looking at https://github.com/dandi/dandi-schema/blob/master/dandischema/metadata.py#L461 we seems to assign new version in

obj_migrated["schemaVersion"] = to_version

only if we change the record, although should always as a result of migration. So plan should

• add/change test so it fails now
• move that assigment out of if block and see that it fixes the issue
  </issue_description>

<agent_instructions>add patch and release labels</agent_instructions>

Comments on the Issue (you are @copilot in this section)

• Fixes bug: migrate would assign target version only for records with schema starting versions under 0.6.0 #353

---

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 97.89%. Comparing base (5cf181a) to head (883d6fb).
⚠️ Report is 9 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master     #354   +/-   ##
=======================================
  Coverage   97.89%   97.89%           
=======================================
  Files          18       18           
  Lines        2370     2377    +7     
=======================================
+ Hits         2320     2327    +7     
  Misses         50       50           

Flag	Coverage Δ
unittests	97.89% <100.00%> (+<0.01%)	⬆️

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[yarikoptic]

@copilot remember running pre-commit when you commit, or otherwise reacting to lints of that CI run

[yarikoptic]

@copilot -- address pre-commit fixes:

trim trailing whitespace.................................................Failed
- hook id: trailing-whitespace
- exit code: 1
- files were modified by this hook

Fixing dandischema/tests/test_metadata.py
Fixing dandischema/metadata.py

and remember to generally prune trailing whitespaces unless they are intentionally added!

[Copilot]

@copilot remember running pre-commit when you commit, or otherwise reacting to lints of that CI run

Fixed trailing whitespace issues flagged by pre-commit in commit 883d6fb. All pre-commit checks pass now.

[yarikoptic]

isn't that what we want to do -- always add target schemaVersion, even if no changes were needed? ;)