Extra `.freeze` left in parsing gemspec files

### Description

> Please leave a brief description of the bug or feature request:

### How To Reproduce

> Tell us how to reproduce the issue.

Run [docker pipeline](https://scancodeio.readthedocs.io/en/latest/scanpipe-tutorial-1.html) in scancode.io on a docker image created by building from this Dockerfile:

```
FROM ubuntu:20.04
RUN apt-get update \
&& DEBIAN_FRONTEND=noninteractive apt-get install -y \
build-essential libyaml-dev libreadline-dev \
zlib1g-dev libncurses5-dev libffi-dev libgdbm6 \
libgdbm-dev libssl-dev libxext6 libxml2-dev \
binutils ca-cacert wget unzip
WORKDIR /tmp
RUN wget --no-check-certificate https://cache.ruby-lang.org/pub/ruby/2.7/ruby-2.7.2.zip \
&& unzip -q ruby-2.7.2.zip \
&& cd /tmp/ruby-2.7.2 \
&& bash configure && make && make install
RUN gem update --no-document --system && gem install --no-document bundle
```

This is essentially a bug in [this function](https://github.com/nexB/scancode-toolkit/blob/develop/src/packagedcode/rubygems.py#L603).

Sample .gemspec file for consideration, taken from `/usr/lib/ruby/gems/2.7.0/specifications/default/benchmark-0.1.0.gemspec` from my local machine.

```
# -*- encoding: utf-8 -*-
# stub: benchmark 0.1.0 ruby lib

Gem::Specification.new do |s|
s.name = "benchmark".freeze
s.version = "0.1.0"

s.required_rubygems_version = Gem::Requirement.new(">= 0".freeze) if s.respond_to? :required_rubygems_version=
s.metadata = { "homepage_uri" => "https://github.com/ruby/benchmark", "source_code_uri" => "https://github.com/ruby/benchmark" } if s.respond_to? :metadata=
s.require_paths = ["lib".freeze]
s.authors = ["Yukihiro Matsumoto".freeze]
s.bindir = "exe".freeze
s.date = "2021-04-15"
s.description = "a performance benchmarking library".freeze
s.email = ["matz@ruby-lang.org".freeze]
s.files = ["benchmark.rb".freeze, "benchmark/version.rb".freeze]
s.homepage = "https://github.com/ruby/benchmark".freeze
s.licenses = ["BSD-2-Clause".freeze]
s.rubygems_version = "3.1.2".freeze
s.summary = "a performance benchmarking library".freeze
end
```

### System configuration

> For bug reports, it really helps us to know:

* What OS are you running on? (Windows/MacOS/Linux) Ubuntu20.04
* What version of scancode-toolkit was used to generate the scan file? 21.3.31
* What installation method was used to install/run scancode? via scancode.io installation