minor #19225 [ci] Upgrade phpunit wrapper deps (nicolas-grekas)

This PR was merged into the 2.7 branch.

Discussion
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[ci] Upgrade phpunit wrapper deps

| Q             | A
| ------------- | ---
| Branch?       | 2.7
| Bug fix?      | no
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | -
| License       | MIT
| Doc PR        | -

To get sebastianbergmann/exporter#14 in.

Commits
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9f916a8 [ci] Upgrade phpunit wrapper deps

Author: nicolas-grekas

phpunit

@@ -11,7 +11,7 @@
  */
 
 // Please update when phpunit needs to be reinstalled with fresh deps:
-// Cache-Id-Version: 2016-03-25 09:45 UTC
+// Cache-Id-Version: 2016-06-29 13:45 UTC
 
 use Symfony\Component\Process\ProcessUtils;