travis: Don't fetch --unshallow when no longer shallow-cloning

Tree-SHA512: a1a6d794431de9639dc985bd42f852f4e11cc2090a826c9a5c2f32658246f5a2a634f113b86ae66bf6222fe3180c3c23145bc297082ff9f61d3abbab5ac53341

.travis.yml

@@ -8,7 +8,7 @@ cache:
   - depends/sdk-sources
   - $HOME/.ccache
 git:
-  depth: false  # full clone for git subtree check
+  depth: false  # full clone for git subtree check, this works around issue #12388
 env:
   global:
     - MAKEJOBS=-j3
@@ -64,7 +64,6 @@ before_script:
     - if [ "$NEED_XVFB" = 1 ]; then export DISPLAY=:99.0; /sbin/start-stop-daemon --start --pidfile /tmp/custom_xvfb_99.pid --make-pidfile --background --exec /usr/bin/Xvfb -- :99 -ac; fi
 script:
     - if [ "$CHECK_DOC" = 1 -a "$TRAVIS_REPO_SLUG" = "bitcoin/bitcoin" -a "$TRAVIS_PULL_REQUEST" = "false" ]; then while read LINE; do travis_retry gpg --keyserver hkp://subset.pool.sks-keyservers.net --recv-keys $LINE; done < contrib/verify-commits/trusted-keys; fi
-    - if [ "$CHECK_DOC" = 1 -a "$TRAVIS_REPO_SLUG" = "bitcoin/bitcoin" -a "$TRAVIS_PULL_REQUEST" = "false" ]; then git fetch --unshallow; fi
     - if [ "$CHECK_DOC" = 1 -a "$TRAVIS_REPO_SLUG" = "bitcoin/bitcoin" -a "$TRAVIS_PULL_REQUEST" = "false" ]; then contrib/verify-commits/verify-commits.sh; fi
     - export TRAVIS_COMMIT_LOG=`git log --format=fuller -1`
     - if [ -n "$USE_SHELL" ]; then export CONFIG_SHELL="$USE_SHELL"; fi