Revert "Remove TEST_BUNDLED_GEMS_ALLOW_FAILURES"

This reverts commit 75e8dd58f6.

We seem to randomly hit another issue these days:
https://github.com/ruby/ruby/runs/368756135
https://github.com/ruby/ruby/runs/368756191

.github/workflows/macos.yml

@@ -63,6 +63,8 @@ jobs:
         run: make -C build $JOBS -s ${{ matrix.test_task }}
         env:
           RUBY_TESTOPTS: "-q --tty=no"
+          # Remove minitest from TEST_BUNDLED_GEMS_ALLOW_FAILURES if https://github.com/seattlerb/minitest/pull/798 is resolved
+          TEST_BUNDLED_GEMS_ALLOW_FAILURES: "minitest"
       - name: Leaked Globals
         run: make -C build -s leaked-globals
       - uses: k0kubun/action-slack@v2.0.0

.github/workflows/ubuntu.yml

@@ -97,6 +97,8 @@ jobs:
         run: make -C build $JOBS -s ${{ matrix.test_task }}
         env:
           RUBY_TESTOPTS: "-q --tty=no"
+          # Remove minitest from TEST_BUNDLED_GEMS_ALLOW_FAILURES if https://github.com/seattlerb/minitest/pull/798 is resolved
+          TEST_BUNDLED_GEMS_ALLOW_FAILURES: "minitest"
       - name: Leaked Globals
         run: make -C build -s leaked-globals
       - uses: k0kubun/action-slack@v2.0.0