Address remaining WordPress PHPUnit test failures

The WordPress PHPUnit test suite passes over 99% tests with SQLite, but some of them are still failing.

Let's look into these failures and see if we can address them:

# Errors
Tests_DB_Charset::test_invalid_characters_in_query
Tests_DB_Charset::test_set_charset_changes_the_connection_collation

# Failures
Tests_Admin_wpSiteHealth::test_object_cache_thresholds with data set #2
Tests_Admin_wpSiteHealth::test_object_cache_thresholds with data set #3
Tests_Comment::test_wp_new_comment_respects_comment_field_lengths
Tests_Comment::test_wp_update_comment
Tests_DB_Charset::test_get_column_charset with data set #0
Tests_DB_Charset::test_get_column_charset with data set #1
Tests_DB_Charset::test_get_column_charset with data set #2
Tests_DB_Charset::test_get_column_charset with data set #3
Tests_DB_Charset::test_get_column_charset with data set #4
Tests_DB_Charset::test_get_column_charset with data set #5
Tests_DB_Charset::test_get_column_charset with data set #6
Tests_DB_Charset::test_get_column_charset with data set #7
Tests_DB_Charset::test_get_column_charset_is_mysql_undefined with data set #0
Tests_DB_Charset::test_get_column_charset_is_mysql_undefined with data set #1
Tests_DB_Charset::test_get_column_charset_is_mysql_undefined with data set #2
Tests_DB_Charset::test_get_column_charset_is_mysql_undefined with data set #3
Tests_DB_Charset::test_get_column_charset_is_mysql_undefined with data set #4
Tests_DB_Charset::test_get_column_charset_is_mysql_undefined with data set #5
Tests_DB_Charset::test_get_column_charset_is_mysql_undefined with data set #6
Tests_DB_Charset::test_get_column_charset_is_mysql_undefined with data set #7
Tests_DB_Charset::test_get_column_charset_non_mysql with data set #0
Tests_DB_Charset::test_get_column_charset_non_mysql with data set #1
Tests_DB_Charset::test_get_column_charset_non_mysql with data set #2
Tests_DB_Charset::test_get_column_charset_non_mysql with data set #3
Tests_DB_Charset::test_get_column_charset_non_mysql with data set #4
Tests_DB_Charset::test_get_column_charset_non_mysql with data set #5
Tests_DB_Charset::test_get_column_charset_non_mysql with data set #6
Tests_DB_Charset::test_get_column_charset_non_mysql with data set #7
Tests_DB_Charset::test_process_field_charsets_on_nonexistent_table
Tests_DB_Charset::test_strip_invalid_text with data set #21
Tests_DB_Charset::test_strip_invalid_text with data set #22
Tests_DB_Charset::test_strip_invalid_text with data set #23
Tests_DB_Charset::test_strip_invalid_text with data set #24
Tests_DB_Charset::test_strip_invalid_text with data set #25
Tests_DB_Charset::test_strip_invalid_text with data set #26
Tests_DB_Charset::test_strip_invalid_text with data set #27
Tests_DB_Charset::test_strip_invalid_text with data set #28
Tests_DB_Charset::test_strip_invalid_text with data set #30
Tests_DB_Charset::test_strip_invalid_text with data set #31
Tests_DB_Charset::test_strip_invalid_text with data set #32
Tests_DB_Charset::test_strip_invalid_text with data set #33
Tests_DB_Charset::test_strip_invalid_text with data set #34
Tests_DB_Charset::test_strip_invalid_text with data set #35
Tests_DB_Charset::test_strip_invalid_text with data set #36
Tests_DB_Charset::test_strip_invalid_text with data set #37
Tests_DB_Charset::test_strip_invalid_text with data set #39
Tests_DB_Charset::test_strip_invalid_text with data set #40
Tests_DB_Charset::test_strip_invalid_text with data set #41
Tests_DB_Charset::test_strip_invalid_text_for_column_bails_if_ascii_input_too_long
Tests_DB_dbDelta::test_spatial_indices
Tests_DB::test_charset_switched_to_utf8mb4
Tests_DB::test_close
Tests_DB::test_delete_value_too_long_for_field with data set "too long"
Tests_DB::test_has_cap
Tests_DB::test_insert_value_too_long_for_field with data set "too long"
Tests_DB::test_mysqli_flush_sync
Tests_DB::test_non_unicode_collations
Tests_DB::test_pre_get_col_charset_filter
Tests_DB::test_process_fields_on_nonexistent_table
Tests_DB::test_process_fields_value_too_long_for_field with data set "too long"
Tests_DB::test_query_value_contains_invalid_chars
Tests_DB::test_replace_value_too_long_for_field with data set "too long"
Tests_DB::test_replace
Tests_DB::test_supports_collation
Tests_DB::test_update_value_too_long_for_field with data set "too long"
Tests_Menu_Walker_Nav_Menu::test_start_el_with_empty_attributes with data set #1
Tests_Menu_Walker_Nav_Menu::test_start_el_with_empty_attributes with data set #2
Tests_Menu_Walker_Nav_Menu::test_start_el_with_empty_attributes with data set #3
Tests_Menu_Walker_Nav_Menu::test_start_el_with_empty_attributes with data set #4
Tests_Menu_Walker_Nav_Menu::test_start_el_with_empty_attributes with data set #5
Tests_Menu_Walker_Nav_Menu::test_start_el_with_empty_attributes with data set #6
Tests_Menu_Walker_Nav_Menu::test_start_el_with_empty_attributes with data set #7
Tests_Menu_wpNavMenu::test_wp_nav_menu_should_not_have_has_children_class_with_custom_depth
WP_Test_REST_Posts_Controller::test_get_items_orderby_modified_query

Start by running the WordPress PHPUnit suite and reviewing the listed errors and failures, especially the Tests_DB_Charset and Tests_DB groups. Group failures by subsystem before investigating their causes. Done means the listed failures are addressed and the suite passes with SQLite.