Gitlab test script fixes (openethereum#8573)

* Exclude /docs from modified files.

* Ensure all references in the working tree are available

* Remove duplicated line from test script

scripts/gitlab-test.sh

@@ -7,8 +7,8 @@ if [[ "$CI_COMMIT_REF_NAME" = "master" || "$CI_COMMIT_REF_NAME" = "beta" || "$CI
 else
   export GIT_COMPARE=master;
 fi
-export RUST_FILES_MODIFIED="$(git --no-pager diff --name-only $GIT_COMPARE...$CI_COMMIT_SHA | grep -v -e ^\\. -e ^LICENSE -e ^README.md -e ^test.sh -e ^windows/ -e ^scripts/ -e ^mac/ -e ^nsis/ | wc -l)"
-echo "RUST_FILES_MODIFIED: $RUST_FILES_MODIFIED"
+git fetch -a
+export RUST_FILES_MODIFIED="$(git --no-pager diff --name-only $GIT_COMPARE...$CI_COMMIT_SHA | grep -v -e ^\\. -e ^LICENSE -e ^README.md -e ^test.sh -e ^windows/ -e ^scripts/ -e ^mac/ -e ^nsis/ -e ^docs/ | wc -l)"
 echo "RUST_FILES_MODIFIED: $RUST_FILES_MODIFIED"
 TEST_SWITCH=$1
 rust_test () {