WEB_EXT_API_APPROVAL_TIMEOUT -> WEB_EXT_APPROVAL_TIMEOUT (#1944)

The "API_" in the environment variable is likely a copy-paste typo from
the preceding section. The correct environment variable to use is
WEB_EXT_APPROVAL_TIMEOUT.

src/content/documentation/develop/web-ext-command-reference.md

@@ -585,7 +585,7 @@ Environment variable: `$WEB_EXT_API_SECRET`
 
 Number of milliseconds to wait for approval before giving up. Set to 0 to disable the wait for approval. Defaults to `timeout` if not set.
 
-Environment variable: `$WEB_EXT_API_APPROVAL_TIMEOUT`
+Environment variable: `$WEB_EXT_APPROVAL_TIMEOUT`
 </section>
 
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