Don't run doctest during tests

Index: crates/ruff_db/Cargo.toml
--- crates/ruff_db/Cargo.toml.orig
+++ crates/ruff_db/Cargo.toml
@@ -57,6 +57,9 @@ etcetera = { workspace = true, optional = true }
 insta = { workspace = true, features = ["filters"] }
 tempfile = { workspace = true }
 
+[lib]
+doctest = false
+
 [features]
 cache = ["ruff_cache"]
 junit = ["dep:quick-junit"]
