Avoid criticizable perl code

Using `require` / `->import` instead of `use` avoids the use of a
"stringy eval", making for cleaner code that we don't need to silence
perlcritic about.

Per Andrew Dunstan

Discussion: https://postgr.es/m/7cd3bbbd-0216-4436-d571-8f80c9259a07@dunslane.net

Author: alvherre

src/test/modules/libpq_pipeline/t/001_libpq_pipeline.pl

@@ -9,16 +9,16 @@
 use Test::More;
 
 # Use Test::Differences if installed, and select unified diff output.
-# No decent way to select a context line count with this;
-# we could use a sub ref to allow that.
 BEGIN
 {
-	#<<< protect next line from pgperltidy
-	if (!eval q{ use Test::Differences; unified_diff(); 1 })    ## no critic (ProhibitStringyEval)
-	#>>>
-	{
-		*eq_or_diff = \&is;
-	}
+	eval {
+		require Test::Differences;
+		Test::Differences->import;
+		unified_diff();
+	};
+
+	# No dice -- fall back to 'is'
+	*eq_or_diff = \&is if $@;
 }
 
 my $node = PostgreSQL::Test::Cluster->new('main');