fix(examples): fix examples uri for sqlite

[villebro]

SUMMARY

The PR #25680 fixed the default sqlite connection string for the metastore connection so that it works correctly in an async use case. However, this fix was not applied to the Examples data URI, causing async access to fail.

TESTING INSTRUCTIONS

1. Install a fresh local devenv using sqlite
2. Enable async execution for the examples database
3. Issue a select 1 on the examples database

ADDITIONAL INFORMATION

• Has associated issue: SIP-143: [SIP-143] Global Async Task Framework #29839
• Required feature flags:
• Changes UI
• Includes DB Migration (follow approval process in SIP-59)
  • Migration is atomic, supports rollback & is backwards-compatible
  • Confirm DB migration upgrade and downgrade tested
  • Runtime estimates and downtime expectations provided
• Introduces new feature or API
• Removes existing feature or API

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 83.75%. Comparing base (76d897e) to head (09212c8).
⚠️ Report is 2203 commits behind head on master.

Additional details and impacted files

@@             Coverage Diff             @@
##           master   #30277       +/-   ##
===========================================
+ Coverage   60.48%   83.75%   +23.27%     
===========================================
  Files        1931      534     -1397     
  Lines       76236    38544    -37692     
  Branches     8568        0     -8568     
===========================================
- Hits        46114    32284    -13830     
+ Misses      28017     6260    -21757     
+ Partials     2105        0     -2105     

Flag	Coverage Δ
hive	∅ <100.00%> (∅)
javascript	?
mysql	∅ <100.00%> (?)
postgres	∅ <100.00%> (?)
presto	∅ <100.00%> (∅)
python	∅ <100.00%> (∅)
sqlite	∅ <100.00%> (?)
unit	∅ <100.00%> (∅)

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[rusackas]

Approved, and restarting E2E failures, but I'm wondering if we need to update this in the tests too.
From superset/.github/workflows/superset-python-integrationtest.yml

  test-sqlite:
    runs-on: ubuntu-22.04
    env:
      PYTHONPATH: ${{ github.workspace }}
      SUPERSET_CONFIG: tests.integration_tests.superset_test_config
      REDIS_PORT: 16379
      SUPERSET__SQLALCHEMY_DATABASE_URI: |
        sqlite:///${{ github.workspace }}/.temp/superset.db?check_same_thread=true
      SUPERSET__SQLALCHEMY_EXAMPLES_URI: |
        sqlite:///${{ github.workspace }}/.temp/examples.db?check_same_thread=true

To take it one step further, is there even a case for check_same_thread=true any more, or can we whittle some code away?