testers.hasPkgConfigModules: Shorten derivation name

Overly long names are annoying, and grab attention that these tests
usually don't need.
Keep it short and sweet.

pkgs/build-support/testers/hasPkgConfigModules/tester.nix

@@ -1,10 +1,20 @@
 # Static arguments
 { lib, runCommand, pkg-config }:
 
+let
+  genTestName = moduleNames:
+    # An overly long name made the progress bar weird and distraction, and same
+    # for the build log prefix.
+    if lib.length moduleNames > 1 then
+      "modules"
+    else
+      lib.head moduleNames;
+in
+
 # Tester arguments
 { package,
   moduleNames ? package.meta.pkgConfigModules,
-  testName ? "check-pkg-config-${lib.concatStringsSep "-" moduleNames}",
+  testName ? "check-pkg-config-${genTestName moduleNames}",
   version ? package.version or null,
   versionCheck ? false,
 }: