chore(deps): update dependency com.google.appengine:appengine-api-1.0-sdk to v1.9.88 (googleapis#591)

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This PR contains the following updates:

| Package | Change | Age | Adoption | Passing | Confidence |
|---|---|---|---|---|---|
| com.google.appengine:appengine-api-1.0-sdk | `1.9.86` -> `1.9.88` | [![age](https://badges.renovateapi.com/packages/maven/com.google.appengine:appengine-api-1.0-sdk/1.9.88/age-slim)](https://docs.renovatebot.com/merge-confidence/) | [![adoption](https://badges.renovateapi.com/packages/maven/com.google.appengine:appengine-api-1.0-sdk/1.9.88/adoption-slim)](https://docs.renovatebot.com/merge-confidence/) | [![passing](https://badges.renovateapi.com/packages/maven/com.google.appengine:appengine-api-1.0-sdk/1.9.88/compatibility-slim/1.9.86)](https://docs.renovatebot.com/merge-confidence/) | [![confidence](https://badges.renovateapi.com/packages/maven/com.google.appengine:appengine-api-1.0-sdk/1.9.88/confidence-slim/1.9.86)](https://docs.renovatebot.com/merge-confidence/) |

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pom.xml

@@ -62,7 +62,7 @@
     <project.google.http.version>1.39.2</project.google.http.version>
     <project.junit.version>4.13.2</project.junit.version>
     <project.guava.version>30.1.1-android</project.guava.version>
-    <project.appengine.version>1.9.86</project.appengine.version>
+    <project.appengine.version>1.9.88</project.appengine.version>
     <project.autovalue.version>1.7.4</project.autovalue.version>
     <project.findbugs.version>3.0.2</project.findbugs.version>
     <deploy.autorelease>false</deploy.autorelease>