Specify exact version for assert_cmd and predicates

Since their official MSRV is at 1.54, while ours is 1.48, any patch
update might break our MSRV! To prevent this specify a
specific version.

Signed-off-by: Jonathan Schwender <schwenderjonathan@gmail.com>

Cargo.toml

@@ -94,11 +94,11 @@ void = { version = "1", optional = true }
 version-compare = { version = "0.0.11", optional = true }
 
 [dev-dependencies]
-assert_cmd = "2.0.4"
+assert_cmd = "=2.0.4"
 cc = "1.0"
 chrono = "0.4"
 itertools = "0.10"
-predicates = "2.1.1"
+predicates = "=2.1.1"
 thirtyfour_sync = "0.27"
 
 [target.'cfg(unix)'.dependencies]