Fixes #1047.

MakoLexer is only registered for *.mao. Most Mako templates in the wild use .mako: Pyramid's pyramid_mako templates, Alembic's script.py.mako, and GitHub Linguist lists both .mako and .mao for Mako. So filename-based lookup fails for them:

>>> from pygments.lexers import get_lexer_for_filename
>>> get_lexer_for_filename('index.mako')
pygments.util.ClassNotFound: no lexer for filename 'index.mako' found

Fix: I added *.mako to MakoLexer.filenames and kept *.mao, then regenerated _mapping.py with scripts/gen_mapfiles.py. Only the Mako line changed. No other lexer claims *.mako. This follows the other template families, where the base lexer owns the base extension (CheetahLexer has *.tmpl, MyghtyLexer has *.myt, VelocityLexer has *.vm).

Tests: I added test_mako_filenames to tests/test_templates.py for index.mako, script.py.mako and test.mao. The two .mako cases fail on master and pass with the fix. The full suite passes (pytest tests --ignore=tests/contrast: 5332 passed, 16 skipped). I skipped tests/contrast because wcag_contrast_ratio isn't installed in my environment.

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