[skip ci] Allow to run push workflows manually

As is, we're running the push workflow for all pushes and pull request,
plus we run more comprehensive nightly workflow for all branches which
had commits during the day.  That means that security branches may not
run CI for weeks or even months.  In the meantime, dependencies might
be updated, which can cause later workflow runs to fail.  For instance,
a few openssl tests fail due to security fixes in OpenSSL[1], an update
of Oracle Instant Client causes a couple of oci8 and pdo_oci tests to
fail[2], and the macOS builds do no longer even built (investigation
pending).

Therefore, we allow to run the pull workflow manually, so it is
possible to check the CI condition of temporary inactive branches from
time to time.

[1] <https://github.com/php/php-src/pull/16097>
[2] <https://github.com/php/php-src/pull/16107>

Closes GH-16148.

.github/workflows/push.yml

@@ -33,6 +33,7 @@ on:
       - .circleci/*
     branches:
       - '**'
+  workflow_dispatch: ~
 concurrency:
   group: ${{ github.workflow }}-${{ github.event.pull_request.url || github.run_id }}
   cancel-in-progress: true