Don't use parking_lot versions newer than 0.12.4

Signed-off-by: Simon Wülker <simon.wuelker@arcor.de>

Author: simonwuelker

Cargo.toml

@@ -36,6 +36,10 @@ string_cache = "0.9.0"
 string_cache_codegen = "0.6.1"
 utf-8 = "0.7"
 
+# parking_lot is a transitive dependency, but we need to pin it here because
+# 0.12.5 bumps the MSRV past our MSRV (1.70 at the time of writing).
+parking_lot = ">= 0.12, < 0.12.5"
+
 # Dev dependencies
 criterion = "0.7"
 env_logger = "0.10"