Remove the GC build check in Ubuntu.yml

Merged: https://github.com/ruby/ruby/pull/12212

.github/workflows/ubuntu.yml

@@ -33,9 +33,6 @@ jobs:
             configure: '--disable-yjit'
           - test_task: check
             configure: '--enable-shared --enable-load-relative'
-          - test_task: check
-            modular_gc: true
-            configure: '--with-modular-gc=/home/runner/ruby_gc'
           - test_task: test-bundler-parallel
             timeout: 50
           - test_task: test-bundled-gems
@@ -99,13 +96,6 @@ jobs:
 
       - run: $SETARCH make
 
-      - name: Build modular GC
-        run: |
-          echo "RUBY_GC_LIBRARY=default" >> $GITHUB_ENV
-          make modular-gc MODULAR_GC=default
-          make distclean-modular-gc MODULAR_GC=default
-        if: ${{ matrix.modular_gc }}
-
       - run: |
           $SETARCH make golf
           case "${{ matrix.configure }}" in