(travis) Do not run the git authorship check within a github PR

Before running the CI test github "helpfully" generates a merge-commit,
which uses the email as listed in the github profile, NOT using the
email/name as seen on the merged commit itself. This can cause the entire
thing to fail for no apparent reason

Since any PR is scrutinized and tested to bits after the fact - skipping
the test is safe

Read under -w

xt/dist/authors.t

@@ -58,16 +58,29 @@ if (length $ENV{PATH}) {
   ) =~ /\A(.+)\z/;
 }
 
-# this may fail - not every system has git
-if (my @git_authors = map
-  { my ($gitname) = m/^ \s* \d+ \s* (.+?) \s* $/mx; utf8::decode($gitname); $gitname }
-  qx( git shortlog -e -s )
+# no git-check when smoking a PR
+if (
+  (
+    ! $ENV{TRAVIS_PULL_REQUEST}
+      or
+    $ENV{TRAVIS_PULL_REQUEST} eq "false"
+  )
+    and
+  -d '.git'
 ) {
-  for (@git_authors) {
+
+  binmode (Test::More->builder->$_, ':utf8') for qw/output failure_output todo_output/;
+
+  # this may fail - not every system has git
+  for (
+    map
+      { my ($gitname) = m/^ \s* \d+ \s* (.+?) \s* $/mx; utf8::decode($gitname); $gitname }
+      qx( git shortlog -e -s )
+  ) {
     my ($eml) = $_ =~ $email_re;
 
-    fail "Commit author '$_' (from git) not reflected in AUTHORS, perhaps a missing .mailmap entry?"
-      unless $known_authors{$eml};
+    ok $known_authors{$eml},
+      "Commit author '$_' (from .mailmap-aware `git shortlog -e -s`) reflected in ./AUTHORS";
   }
 }