Bump version to 1.15.0 (#537)

Note that the 1.14.1rc1 release was yanked because it was accidentally
done on the `main` branch rather than `1.14` branch.

Normally we'd do 1.15.0rc1, but we go straight to 1.15.0 since we
already did 1.14.1rc1 and it was fine.

src/qiskit_sphinx_theme/__init__.py

@@ -22,7 +22,7 @@
     import sphinx.application
     import sphinx.config
 
-__version__ = "1.14.1rc1"
+__version__ = "1.15.0"
 __version_full__ = __version__