PULL_REQUEST_TEMPLATE.md: "Zlib" should not be capitalized.

.github/PULL_REQUEST_TEMPLATE.md

@@ -1,4 +1,4 @@
-- [ ] I confirm that I am the author of this code and release it to the SDL project under the Zlib license. This contribution does not contain code from other sources, including code generated by a Large Language Model ("AI").
+- [ ] I confirm that I am the author of this code and release it to the SDL project under the zlib license. This contribution does not contain code from other sources, including code generated by a Large Language Model ("AI").
 
 <!--- Provide a general summary of your changes in the Title above -->