Fix method used to install dependencies for testing

Without this, there can be gpg errors when checking the signature for
the seq package from ELPA.

run-tests.sh

@@ -8,11 +8,11 @@ INIT_PACKAGE_EL="(progn \
   (require 'package) \
   (push '(\"melpa\" . \"https://melpa.org/packages/\") package-archives) \
   (package-initialize) \
-  (unless package-archive-contents \
-     (package-refresh-contents)) \
   (dolist (pkg '(${NEEDED_PACKAGES})) \
     (unless (package-installed-p pkg) \
-      (package-install pkg))))"
+      (unless (assoc pkg package-archive-contents) \
+        (package-refresh-contents)) \
+      (package-install pkg)))))"
 
 # Refresh package archives, because the test suite needs to see at least
 # package-lint and cl-lib.