tests: relax bad_crate_type to only match error message prefix

So that the cargo test isn't sensitive to suggestions for known crate
types that a rustc PR <rust-lang/rust#134720> is
trying to add.

tests/testsuite/bad_config.rs

@@ -427,7 +427,7 @@ fn bad_crate_type() {
 Caused by:
   process didn't exit successfully: `rustc - --crate-name ___ --print=file-names --crate-type bad_type` ([EXIT_STATUS]: 1)
   --- stderr
-  [ERROR] unknown crate type: `bad_type`
+  [ERROR] unknown crate type: `bad_type`[..]
 
 
 "#]])