Missing GC root somewhere

[Keno]

We have a missing GC root somewhere, as seen on CI https://build.julialang.org/#/builders/77/builds/1618/steps/8/logs/stdio

Please submit a bug report with steps to reproduce this fault, and any error messages that follow (in their entirety). Thanks.
Exception: EXCEPTION_ACCESS_VIOLATION at 0x70532ab4 -- gc_try_setmark at /cygdrive/d/buildbot/worker/package_win32/build/src\gc.c:1643 [inlined]
gc_mark_scan_obj8 at /cygdrive/d/buildbot/worker/package_win32/build/src\gc.c:1837 [inlined]
gc_mark_loop at /cygdrive/d/buildbot/worker/package_win32/build/src\gc.c:2118
in expression starting at loading.jl:1267
gc_try_setmark at /cygdrive/d/buildbot/worker/package_win32/build/src\gc.c:1643 [inlined]
gc_mark_scan_obj8 at /cygdrive/d/buildbot/worker/package_win32/build/src\gc.c:1837 [inlined]
gc_mark_loop at /cygdrive/d/buildbot/worker/package_win32/build/src\gc.c:2118
_jl_gc_collect at /cygdrive/d/buildbot/worker/package_win32/build/src\gc.c:2903
jl_gc_collect at /cygdrive/d/buildbot/worker/package_win32/build/src\gc.c:3109
maybe_collect at /cygdrive/d/buildbot/worker/package_win32/build/src\gc.c:828 [inlined]
jl_gc_pool_alloc at /cygdrive/d/buildbot/worker/package_win32/build/src\gc.c:1143 [inlined]
jl_gc_alloc_ at /cygdrive/d/buildbot/worker/package_win32/build/src\julia_internal.h:277 [inlined]
jl_gc_alloc at /cygdrive/d/buildbot/worker/package_win32/build/src\gc.c:3151
jl_alloc_svec_uninit at /cygdrive/d/buildbot/worker/package_win32/build/src\simplevector.c:60
inst_datatype_inner at /cygdrive/d/buildbot/worker/package_win32/build/src\jltypes.c:1396
inst_datatype_env at /cygdrive/d/buildbot/worker/package_win32/build/src\jltypes.c:895 [inlined]
inst_datatype_env at /cygdrive/d/buildbot/worker/package_win32/build/src\jltypes.c:899 [inlined]
inst_datatype_env at /cygdrive/d/buildbot/worker/package_win32/build/src\jltypes.c:899 [inlined]
inst_datatype_env at /cygdrive/d/buildbot/worker/package_win32/build/src\jltypes.c:899 [inlined]