doc: fix spelling in v8.8.0 changelog

I hear that varible has an a in it.

PR-URL: nodejs/node#16477
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Gireesh Punathil <gpunathi@in.ibm.com>

doc/changelogs/CHANGELOG_V8.md

@@ -43,7 +43,7 @@
   - expose ECDH class [#8188](https://github.com/nodejs/node/pull/8188)
 * **http2**:
   - http2 is now exposed by default without the need for a flag [#15685](https://github.com/nodejs/node/pull/15685)
-  - a new environment varible NODE\_NO\_HTTP2 has been added to allow userland http2 to be required [#15685](https://github.com/nodejs/node/pull/15685)
+  - a new environment variable NODE\_NO\_HTTP2 has been added to allow userland http2 to be required [#15685](https://github.com/nodejs/node/pull/15685)
   - support has been added for generic `Duplex` streams [#16269](https://github.com/nodejs/node/pull/16269)
 * **module**:
   - resolve and instantiate loader pipeline hooks have been added to the ESM lifecycle [#15445](https://github.com/nodejs/node/pull/15445)