Update base64 requirement from ~> 0.2.0 to ~> 0.3.0

Updates the requirements on [base64](https://github.com/ruby/base64) to permit the latest version.
- [Release notes](https://github.com/ruby/base64/releases)
- [Commits](ruby/base64@v0.2.0...v0.3.0)

---
updated-dependencies:
- dependency-name: base64
  dependency-version: 0.3.0
  dependency-type: direct:production
...

Signed-off-by: dependabot[bot] <[email protected]>

Author: dependabot[bot]

Gemfile

@@ -9,6 +9,6 @@ gem "rubocop", "~> 1.75", require: false
 gem "rubocop-performance", "~> 1.25", require: false
 gem "rubocop-rake", "~> 0.7", require: false
 gem "rubocop-rspec", "~> 3.6", require: false
-gem "base64", "~> 0.2.0"
+gem "base64", "~> 0.3.0"
 gem "bigdecimal", "~> 3.1"
 gem "csv", "~> 3.2"