erb: Update 4.0.2->4.0.3.1

[Sharpie]

This commit upgrades the default erb gem in Ruby 3.2.11 from the original version of 4.0.2 to 4.0.3.1. This release contains a fix for the following high-severity issue:

GHSA-q339-8rmv-2mhv

There will be no further releases to Ruby 3.2, thus this patch was assembled by checking out v3_2_11 of the ruby/ruby repository and using their tooling to sync commits:

./tool/sync_default_gems.rb -e erb c2861a81634ff7f236fcd1ec42498e7be0ec44dd...b6be29fd0e0f5089447d2f8d18140ae78258621d

This corresponds to the following changeset in the ruby/erb repository:

ruby/erb@v4.0.2...v4.0.3.1

CVE-2026-41316: https://nvd.nist.gov/vuln/detail/CVE-2026-41316

Checklist

I have:

• read the CONTRIBUTING.md document
• read and accepted the Developer Certificate of Origin document and added a Signed-off-by annotation to each of my commits
• tested this code
• included documentation (including possible behaviour changes)
• documented the code
• added or modified regression test(s)
• added or modified unit test(s)

[bastelfreak]

I like the idea of patching the gem instead of installing a second version of it. That always introduces weird site effects. Nice job!

[Sharpie]

Installing a second version isn't a complete fix as security scanners will still report a CVE finding if they see the old .gemspec file.