Build/Test Tools: Make the WordPress installation E2E test repeatable

[devsupportlogicrays]

Description

tests/e2e/specs/install.test.js rewrites $table_prefix to wp_e2e_ so WordPress enters the install wizard, but it never dropped the tables that install creates. After the first green run, leftover wp_e2e_* tables make every later run treat the site as already installed, so the test never reaches /wp-admin/install.php.

This change:

• Extracts table cleanup into a dropTestInstallTables() helper that drops the standard single-site tables under TEST_TABLE_PREFIX via wp eval / $wpdb (avoids shelling out to the mysql client).
• Runs that helper before the prefix swap in beforeEach and again in afterEach teardown, so stale tables cannot short-circuit the wizard on the first attempt.
• Exits non-zero when any $wpdb->query() returns false, so failed cleanup cannot leave the suite green.
• Retries page.goto('/') with expect(...).toPass() so navigation itself retries after the host-side wp-config.php rewrite (Docker bind-mount lag).
• Also fixes the missing semicolon after .check() in the install form fill.

This builds on the approach discussed in #13302 and incorporates the review feedback there (helper extraction, cleanup before the prefix change, and failing on false query results).

Testing Instructions

1. Ensure the local env is running (npm run env:start).
2. Optionally leave stale tables behind once:

   npm run test:e2e -- tests/e2e/specs/install.test.js
   

3. Run the same file again (and a third time). All runs should pass and land on install.php without manual DROP TABLE cleanup.
4. To confirm cleanup failure handling, temporarily break a table name in TEST_INSTALL_TABLES and confirm the helper exits non-zero.

Trac ticket: https://core.trac.wordpress.org/ticket/65982

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