Test fixes for 3.15 (GH-133599)

Followup to 942673ed194813015d98819cfae7eba78ba5e1f9 (GH-133588)

* Update configure for Python 3.15

* Update magic number for 3.15

* Remove deprecated 'check_home' argument from sysconfig.is_python_build

* Add warningignore entries for Modules/_sqlite/clinic/connection.c.h

* Work around c-analyzer complaints about _testclinic deprecation tests

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Co-authored-by: Hugo van Kemenade <1324225+hugovk@users.noreply.github.com>