Fix a panic when parsing var patterns

cranelift/isle/Cargo.lock

@@ -115,6 +115,15 @@ dependencies = [
  "log",
 ]
 
+[[package]]
+name = "env_logger"
+version = "0.9.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "0b2cf0344971ee6c64c31be0d530793fba457d322dfec2810c453d0ef228f9c3"
+dependencies = [
+ "log",
+]
+
 [[package]]
 name = "gimli"
 version = "0.25.0"
@@ -158,15 +167,17 @@ dependencies = [
 name = "isle-fuzz"
 version = "0.0.0"
 dependencies = [
+ "env_logger 0.9.0",
  "isle",
  "libfuzzer-sys",
+ "log",
 ]
 
 [[package]]
 name = "islec"
 version = "0.1.0"
 dependencies = [
- "env_logger",
+ "env_logger 0.8.4",
  "isle",
  "log",
  "miette",