Fix spacing for SelectPanel header on modal to better align with x button (#5962)

Co-authored-by: francinelucca <40550942+francinelucca@users.noreply.github.com>

Author: emilybrick

.changeset/long-boats-swim.md

@@ -0,0 +1,5 @@
+---
+'@primer/react': patch
+---
+
+Fix spacing for SelectPanel header on modal to better align with x button 

.playwright/snapshots/components/SelectPanel.test.ts-snapshots/SelectPanel-Multi-Select-Modal-dark-colorblind-linux.png

@@ -24,6 +24,10 @@
   font-size: var(--text-body-size-medium);
 }
 
+.Wrapper[data-variant='modal'] .Title {
+  margin-top: var(--base-size-8); /* styling specific to the modal variant */
+}
+
 .Subtitle {
   margin-left: var(--base-size-8);
   font-size: var(--text-body-size-small);