minor #33963 Add .gitignore to .gitattributes (reedy)

This PR was merged into the 4.4 branch.

Discussion
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Add .gitignore to .gitattributes

| Q             | A
| ------------- | ---
| Branch?       | 4.4
| Bug fix?      | yes
| New feature?  | no
| Deprecations? | no
| Tickets       | #33946
| License       | MIT

Commits
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246c5fdf43 Add .gitignore to .gitattributes

Author: fabpot

.gitattributes

@@ -1,2 +1,3 @@
 /Tests export-ignore
 /phpunit.xml.dist export-ignore
+/.gitignore export-ignore