[11.x] Fix adding constraints on sqlite

[hafezdivandari]

SQLite schema grammar silently ignores adding primary key and foreign key constraints when altering table, this PR fixes that. I understand that this was to preventing failure when running tests using SQLite, but please consider that it's more important to let the user know that these constraints are not actually added. A simple workaround for users that use SQLite for running tests is to simply check for their database before adding constraints:

Schema::table('posts', function (Blueprint $table) {
    // ...

    if (! Schema::getConnection() instanceof \Illuminate\Database\SQLiteConnection) {
        $table->foreign('user_id')->references('id')->on('users');
    }
});

Or alternatively if #49723 merged:

Schema::table('posts', function (Blueprint $table) {
    // ...

    if (! DB::is('sqlite')) {
        $table->foreign('user_id')->references('id')->on('users');
    }
});

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[taylorotwell]

I don't see a big reason to change this atm.

[hafezdivandari]

@taylorotwell this was to fix a long time issue #24876