ENH: use the same capitalization for all error messages

Author: dnicolodi

mesonpy/__init__.py

@@ -750,7 +750,7 @@ def __init__(
         # prepare environment
         self._ninja = _env_ninja_command()
         if self._ninja is None:
-            raise ConfigError(f'Could not find ninja version {_NINJA_REQUIRED_VERSION} or newer.')
+            raise ConfigError(f'could not find ninja version {_NINJA_REQUIRED_VERSION} or newer.')
         self._env.setdefault('NINJA', self._ninja)
 
         # setuptools-like ARCHFLAGS environment variable support
@@ -759,7 +759,7 @@ def __init__(
             if archflags is not None:
                 arch, *other = filter(None, (x.strip() for x in archflags.split('-arch')))
                 if other:
-                    raise ConfigError(f'Multi-architecture builds are not supported but $ARCHFLAGS={archflags!r}')
+                    raise ConfigError(f'multi-architecture builds are not supported but $ARCHFLAGS={archflags!r}')
                 macver, _, nativearch = platform.mac_ver()
                 if arch != nativearch:
                     x = self._env.setdefault('_PYTHON_HOST_PLATFORM', f'macosx-{macver}-{arch}')