.github/workflows/rspec.yml in fontist-1.11.3 vs .github/workflows/rspec.yml in fontist-1.11.5

@@ -12,10 +12,10 @@
     continue-on-error: ${{ matrix.experimental }}
     strategy:
       fail-fast: false
       matrix:
         ruby: [ '2.4', '2.5', '2.6', '2.7', '3.0' ]
-        os: [ ubuntu-latest, windows-latest, macos-latest ]
+        os: [ ubuntu-18.04, ubuntu-latest, windows-latest, macos-latest ]
         experimental: [ false ]
 
     steps:
       - uses: actions/checkout@master
 
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