CI: Trigger gems' child pipelines when Gemfile.lock changes

What does this MR do and why?

Because vendored gems can depend on each other we need to refresh its Gemfile.lock whenever the monorepo Gemfile.lock has changed.

Checking gems/*/Gemfile.lock is unnecessary because each change of an runtime dependency is also reflected in monorepo's Gemfile.lock.

Closes #417428 (closed).

How to validate on CI

1. Update gems/gitlab-rspec/gitlab-rspec.gemspec and run bundle in gems/gitlab-rspec and monorepo's root
2. Commit and push:

diff --git a/Gemfile.lock b/Gemfile.lock
index 4597ca23eb76..cca810b815e9 100644
--- a/Gemfile.lock
+++ b/Gemfile.lock
@@ -38,7 +38,7 @@ PATH
   specs:
     gitlab-rspec (0.1.0)
       activesupport (>= 6.1, < 8)
-      rspec (~> 3.0)
+      rspec (~> 3.1)
 
 PATH
   remote: gems/gitlab-safe_request_store
diff --git a/gems/gitlab-rspec/Gemfile.lock b/gems/gitlab-rspec/Gemfile.lock
index 7d07ad441acd..88d11da21f0e 100644
--- a/gems/gitlab-rspec/Gemfile.lock
+++ b/gems/gitlab-rspec/Gemfile.lock
@@ -3,7 +3,7 @@ PATH
   specs:
     gitlab-rspec (0.1.0)
       activesupport (>= 6.1, < 8)
-      rspec (~> 3.0)
+      rspec (~> 3.1)
 
 GEM
   remote: https://rubygems.org/
diff --git a/gems/gitlab-rspec/gitlab-rspec.gemspec b/gems/gitlab-rspec/gitlab-rspec.gemspec
index 8e41e5436e68..15bb316ab079 100644
--- a/gems/gitlab-rspec/gitlab-rspec.gemspec
+++ b/gems/gitlab-rspec/gitlab-rspec.gemspec
@@ -19,7 +19,7 @@ Gem::Specification.new do |spec|
   spec.require_paths = ["lib"]
 
   spec.add_runtime_dependency "activesupport", ">= 6.1", "< 8"
-  spec.add_runtime_dependency "rspec", "~> 3.0"
+  spec.add_runtime_dependency "rspec", "~> 3.1"
 
   spec.add_development_dependency "factory_bot_rails", "~> 6.2.0"
   spec.add_development_dependency "gitlab-styles", "~> 10.1.0"

3. See CI triggering all child pipelines for gems/ and see them 🔴 fail - https://gitlab.com/gitlab-org/gitlab/-/pipelines/1045887437 (test MR)
   • This replicates !134777 (merged)

https://gitlab.com/gitlab-org/gitlab/-/pipelines/1045880657

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.