Skip custom magic file test on macOS in Azure

Something weird has started happening there with the homebrew libmagic. See
https://dev.azure.com/houseabsolute/e1e160eb-4790-4fee-b545-2e332bfbf407/_apis/build/builds/1350/logs/55
for an example. Excerpt ...

2020-08-29T02:45:49.8707040Z # Found magic file at /usr/share/file/magic.mgc
2020-08-29T02:45:49.8725880Z /Users/runner/work/1/extracted-dist/t/samples/magic, 2: Warning: using regular magic file `/usr/share/file/magic.mgc'
2020-08-29T02:45:49.8727190Z /usr/share/file/magic.mgc, 1: Warning: offset `�����' invalid
2020-08-29T02:45:49.8727800Z /usr/share/file/magic.mgc, 2: Warning: offset `
2020-08-29T02:45:49.8728870Z Version=' invalid
2020-08-29T02:45:49.8729850Z /usr/share/file/magic.mgc, 7: Warning: offset `Firmware v' invalid
2020-08-29T02:45:49.8730910Z /usr/share/file/magic.mgc, 8: Warning: offset `�' invalid
2020-08-29T02:45:49.8732000Z /usr/share/file/magic.mgc, 9: Warning: offset `�' invalid
2020-08-29T02:45:49.8733000Z /usr/share/file/magic.mgc, 14: Warning: offset `�' invalid
2020-08-29T02:45:49.8734570Z /usr/share/file/magic.mgc, 15: Warning: offset `�' invalid

Author: autarch

t/oo-api.t

@@ -54,6 +54,10 @@ SKIP:
     skip 'Could not find the standard magic file', 1
         unless $standard_file;
 
+    skip
+        'Something weird and broken is happening when using the homebrew libmagic in Azure'
+        if $^O eq 'darwin' && $ENV{CI_WORKSPACE_DIRECTORY};
+
     my %custom = (
         'foo.foo' => [
             'A foo file',