Add a feature test, that checks if it runs under Github Actions

related: actions/runner-images#11512

Signed-off-by: Christian Brabandt <[email protected]>

Author: chrisbra

src/testdir/check.vim

@@ -291,4 +291,11 @@ func CheckAllOf(...)
   endfor
 endfunc
 
+" Check if running under Github Actions
+command CheckGithubActions call CheckGithubActions()
+func CheckGithubActions()
+  if expand('$GITHUB_ACTIONS') ==# 'true'
+    throw "Skipped: FIXME: this test doesn't work on Github Actions CI"
+  endif
+endfunc
 " vim: shiftwidth=2 sts=2 expandtab