Blankslate: Reverting icon color to fgColor-muted (#5773)

Co-authored-by: Josh Black <[email protected]>
Co-authored-by: lukasoppermann <[email protected]>

Author: lukasoppermann

.changeset/many-toys-prove.md

@@ -0,0 +1,5 @@
+---
+"@primer/react": patch
+---
+
+Update icon color for Blankslate to `--fgColor-muted` to align with Figma and Primer ViewComponents

.playwright/snapshots/components/Blankslate.test.ts-snapshots/Blankslate-Default-primer-breakpoint-xs-linux.png

@@ -72,6 +72,7 @@
   .Visual {
     max-width: var(--base-size-24);
     margin-bottom: var(--base-size-8);
+    color: var(--fgColor-muted);
 
     & svg {
       width: 100%;