Fix some issues reported by lintian

Fix some issues reported by lintian

• Update lintian override info format in d/source.lintian-overrides on line 4. (mismatched-override)
• Trim trailing whitespace. (trailing-whitespace)
• Use secure copyright file specification URI. (insecure-copyright-format-uri)
• debian/copyright: use spaces rather than tabs to start continuation lines. (tab-in-license-text)
• Move source package lintian overrides to debian/source. (old-source-override-location)

This merge proposal was created by the Janitor bot, and it will automatically rebase or close this proposal as appropriate when the target branch changes. Any comments you leave here will be read by the Janitor's maintainers.

Build and test logs for this branch can be found at https://janitor.debian.net/lintian-fixes/pkg/php-mongodb/7d599c34-07ee-47fa-a80b-8b4027e1a55a.

debian/source/lintian-overrides

 # Override invalid PHP license problem for PHP extensions coming from PECL.PHP.NET
 php-mongodb source: license-problem-php-license *
 # Somehow lintian still can't detect public-domain license
-php-mongodb source: missing-license-paragraph-in-dep5-copyright public-domain *
+php-mongodb source: missing-license-paragraph-in-dep5-copyright public-domain [debian/copyright:*]