Mention that an API bump must be done with RC1

It's okay to change the API change up until the first release candidate only,
and it may not be changed afterwards.

There is a discussion at https://github.com/php/php-src/pull/4470/files that
never resulted in a fix.

/cc @sgolemon @carusogabriel

Author: derickr

docs/release-process.md

@@ -93,11 +93,12 @@
     beta. Do not use dashes, you should `#define PHP_VERSION "7.4.22RC1"` and
     not `#define PHP_VERSION "7.4.22-RC1"`.
 
-    When releasing the first alpha version, bump also API version numbers in
-    `Zend/zend_extensions.h`, `Zend/zend_modules.h`, and `main/php.h`. The API
-    versions between the alpha/beta/.0RCx releases can be left the same or
-    bumped as little as possible because PHP extensions will need to be rebuilt
-    with each bump.
+    When releasing the first release candidate, you must also bump the API
+    version numbers in `Zend/zend_extensions.h`, `Zend/zend_modules.h`, and
+    `main/php.h`. The API versions between the alpha/beta/.0RCx releases can be
+    left the same, or bumped as little as possible because PHP extensions will
+    need to be rebuilt with each bump. Do *not* bump the API versions after
+    RC1.
 
  6. Compile and run `make test`, with and without ZTS, using the right Bison and
     re2c version (for PHP 7.4, minimum Bison 3.0.0 and re2c 0.13.4 are used).