Invoke `rake gensym` for GitHub action build.

.github/workflows/build.yml

@@ -32,7 +32,7 @@ jobs:
     - name: apt
       run: sudo apt install ruby gperf gcc g++
     - name: build and test
-      run: rake -m -j4 all test
+      run: rake -m -j4 gensym all test
       env:
         MRUBY_TARGET: travis
         CC: gcc
@@ -49,7 +49,7 @@ jobs:
     - name: apt
       run: sudo apt install ruby gperf
     - name: build and test
-      run: rake -m -j4 all test
+      run: rake -m -j4 gensym all test
       env:
         MRUBY_TARGET: travis
         CC: clang
@@ -75,7 +75,7 @@ jobs:
     - name: chocolatey
       run: choco install -y ruby gperf
     - name: build
-      run: rake -E 'STDOUT.sync=true' test
+      run: rake -E 'STDOUT.sync=true' -j4 gensym test
       env:
         MRUBY_TARGET: travis
         CFLAGS: -g -O1 -Wall -Wundef
@@ -106,7 +106,7 @@ jobs:
         MRUBY_TARGET: travis
     - name: test
       shell: cmd
-      run: C:\tools\cygwin\bin\ruby.exe /usr/bin/rake -m -j4 -v -E 'STDOUT.sync=true' test
+      run: C:\tools\cygwin\bin\ruby.exe /usr/bin/rake -E 'STDOUT.sync=true' gensym test
       env:
         MRUBY_TARGET: travis
 
@@ -120,7 +120,7 @@ jobs:
       shell: cmd
       run: |
         call "C:\Program Files (x86)\Microsoft Visual Studio\2019\Enterprise\VC\Auxiliary\Build\vcvars64.bat"
-        rake -E "STDOUT.sync=true" test
+        rake -E "STDOUT.sync=true" gensym all test
       env:
         MRUBY_TARGET: appveyor
         # TODO(take-cheeze): Re-enable /O2