Revert "cygwin: disable CI until cygwin fix signal handling"

Cygwin 3.5.6 has been released.

3.5.6 has it's own problems, but they don't appear to have an effect
on our tests.

This reverts commit e7475a1.

.github/workflows/testsuite.yml

@@ -563,14 +563,13 @@ jobs:
   # | (__| |_| | (_| |\ V  V /| | | | |
   #  \___|\__, |\__, | \_/\_/ |_|_| |_|
   #       |___/ |___/
-  # disabled until cygwin get a signal handling fix out
 
   cygwin:
     name: "cygwin"
     runs-on: windows-2019
     timeout-minutes: 120
     needs: sanity_check
-    if: (! cancelled() && (needs.sanity_check.outputs.ci_force_cygwin == 'true'))
+    if: (! cancelled() && (needs.sanity_check.outputs.run_all_jobs == 'true' || needs.sanity_check.outputs.ci_force_cygwin == 'true'))
 
     steps:
       # we use Cygwin git, so no need to configure git here.