Use the bundled bundler

Old bundler used the internal constant of Pathname, that was not
private due to a typo.
ruby/rubygems#9529

Author: nobu

.github/workflows/ubuntu.yml

@@ -251,6 +251,8 @@ jobs:
       - name: Run ruby-bench
         run: ruby run_benchmarks.rb -e "ruby::../build/install/bin/ruby" ${{ matrix.bench_opts }}
         working-directory: ruby-bench
+        env:
+          BUNDLER_VERSION: 0
 
       - uses: ./.github/actions/slack
         with:

.github/workflows/zjit-macos.yml

@@ -225,6 +225,8 @@ jobs:
       - name: Run ruby-bench
         run: ruby run_benchmarks.rb -e "zjit::../build/install/bin/ruby ${{ matrix.ruby_opts }}" ${{ matrix.bench_opts }}
         working-directory: ruby-bench
+        env:
+          BUNDLER_VERSION: 0
 
       - uses: ./.github/actions/slack
         with:

.github/workflows/zjit-ubuntu.yml

@@ -279,6 +279,8 @@ jobs:
       - name: Run ruby-bench
         run: ruby run_benchmarks.rb -e "zjit::../build/install/bin/ruby ${{ matrix.ruby_opts }}" ${{ matrix.bench_opts }}
         working-directory: ruby-bench
+        env:
+          BUNDLER_VERSION: 0
 
       - uses: ./.github/actions/slack
         with: