Fix profiling with tracy. (#5988)

The profiling APIs require a `&str`, but since the label here
is now an `Option<String>`, we must get a `&str` from it.

(cherry picked from commit 20973d1cdc)

# Conflicts:
#	CHANGELOG.md

CHANGELOG.md

@@ -49,6 +49,7 @@ Bottom level categories:
 
 #### General
 
+- Fix profiling with `tracy`. By @waywardmonkeys in [#5988](https://github.com/gfx-rs/wgpu/pull/5988)
 - Fix function for checking bind compatibility to error instead of panic. By @sagudev [#6012](https://github.com/gfx-rs/wgpu/pull/6012)
 - Fix crash when dropping the surface after the device. By @wumpf in [#6052](https://github.com/gfx-rs/wgpu/pull/6052)
 - Fix length of copy in `queue_write_texture`. By @teoxoy in [#6009](https://github.com/gfx-rs/wgpu/pull/6009)

wgpu-core/src/command/render.rs

@@ -1566,7 +1566,7 @@ impl Global {
 
         profiling::scope!(
             "CommandEncoder::run_render_pass {}",
-            base.label.unwrap_or("")
+            base.label.as_deref().unwrap_or("")
         );
 
         let Some(cmd_buf) = pass.parent.as_ref() else {