fix workflow to detect version change

[katebrenner]

What happened:
Right now, the create github release step runs on every push to main

What you expected to happen:
The create github release should only run when a version change is detected.

How to reproduce it (as minimally and precisely as possible):

Screenshots

this is what happens currently if there is no version change & the step runs anyway (the tag & release is labeled as v, instead of a normal release like v0.3.3):

Anything else we need to know?:

Environment:

• Grafana version:
• Sdk version:
• OS Grafana is installed on:
• User OS & Browser:
• Others: