revert back removed assignments

npm_and_yarn/lib/dependabot/npm_and_yarn/package_manager.rb

@@ -200,6 +200,8 @@ class PackageManagerHelper
       def initialize(package_json, lockfiles:)
         @package_json = package_json
         @lockfiles = lockfiles
+        @manifest_package_manager = package_json["packageManager"]
+        @engines = package_json.fetch("engines", nil)
         @package_manager_detector = PackageManagerDetector.new(@lockfiles, @package_json)
       end
 
@@ -216,27 +218,27 @@ def setup(name)
         # i.e. if { engines : "pnpm" : "6" } and { packageManager: "pnpm@6.0.2" },
         # we go for the specificity mentioned in packageManager (6.0.2)
 
-        unless @package_manager_attr&.start_with?("#{name}@") ||
-               (@package_manager_attr&.==name.to_s) ||
-               @package_manager_attr.nil?
+        unless @manifest_package_manager&.start_with?("#{name}@") ||
+               (@manifest_package_manager&.==name.to_s) ||
+               @manifest_package_manager.nil?
           return
         end
 
-        if @engines && @package_manager_attr.nil?
+        if @engines && @manifest_package_manager.nil?
           # if "packageManager" doesn't exists in manifest file,
           # we check if we can extract "engines" information
           version = check_engine_version(name)
 
-        elsif @package_manager_attr&.==name.to_s
+        elsif @manifest_package_manager&.==name.to_s
           # if "packageManager" is found but no version is specified (i.e. pnpm@1.2.3),
           # we check if we can get "engines" info to override default version
           version = check_engine_version(name) if @engines
 
-        elsif @package_manager_attr&.start_with?("#{name}@")
+        elsif @manifest_package_manager&.start_with?("#{name}@")
           # if "packageManager" info has version specification i.e. yarn@3.3.1
           # we go with the version in "packageManager"
           Dependabot.logger.info(
-            "Found \"packageManager\" : \"#{@package_manager_attr}\". Skipped checking \"engines\"."
+            "Found \"packageManager\" : \"#{@manifest_package_manager}\". Skipped checking \"engines\"."
           )
         end
 
@@ -291,9 +293,9 @@ def install(name, version)
       end
 
       def requested_version(name)
-        return unless @package_manager_attr
+        return unless @manifest_package_manager
 
-        match = @package_manager_attr.match(/^#{name}@(?<version>\d+.\d+.\d+)/)
+        match = @manifest_package_manager.match(/^#{name}@(?<version>\d+.\d+.\d+)/)
         return unless match
 
         Dependabot.logger.info("Requested version #{match['version']}")