I've read from numerous remarks that the work I do on that side is not testing, but it is something that complements my testing, it is something that works towards the same goal: valuable, quality software. A happy, skilled developer delivers better results. Being allowed to think, being supported in growing in skills and hearing that you're doing well and improving, they all create a positive cycle.
As a tester, I pay attention to what I get to see in software. Sometimes I see software that doesn't talk to the other pieces of the system - just like the people doing the pieces don't talk. Instead of just reporting the symptoms, I may gently push for a bit of discussions there. Sometimes things barely work, and break more with every attempt to fix. Instead of leaving the developer alone with that, I have the habit of bringing in help they did not request but could use. Sometimes I suspect the code isn't created with a change in mind, and I go the extra mile convincing managers to allow time for team work to change something that works now to something that will work in long term.
Developers seem to appreciate being allowed to refactor - and sometimes what I say makes a big difference on them being allowed to do what they should, or them taking the initiative to do what should be done. And when puzzled on being allowed to go to trainings, I can just choose to say the supporting words out loud, helping people get to trainings they haven't been in for years.
We're in this together. It's just not what my role is, but it's also a lot about who I am as a person. And I'm someone who wants to see the world get better and people be happy.