Baseline the existing mago lint and analyzer findings

Mago is stricter than the PHPStan level 5 baseline it replaces, so the 123
linter and 231 analyzer findings already present are recorded in
lint-baseline.toml and analyzer-baseline.toml, matching the rest of the org.
format --check, lint, analyze and guard all pass, and new findings in new
code still fail.

Author: simon-mundy

.gitattributes

@@ -8,5 +8,7 @@
 /codecov.yml export-ignore
 /infection.json5.dist export-ignore
 /mago.toml export-ignore
+/lint-baseline.toml export-ignore
+/analyzer-baseline.toml export-ignore
 /compose.yml export-ignore
 /docker/ export-ignore