[HUD][dark-mode]: Update JobLinks buttons to use theme variables for dark mode visibility (#6503)

Replaced hardcoded colors with CSS variables in JobLinks.module.css to
ensure buttons are properly visible in dark mode. This improves contrast
and readability of 'Mark unstable job' and related buttons.

Fixes #6500

Original
<img width="1134" alt="image"
src="https://github.com/user-attachments/assets/1a9517b3-688e-48dd-a0bd-cd288dbba1ef"
/>

New
<img width="1138" alt="image"
src="https://github.com/user-attachments/assets/a6ba1fd6-9a7b-48ff-96c6-07c520f7460d"
/>

Author: ZainRizvi

torchci/components/JobLinks.module.css

@@ -1,10 +1,11 @@
 .disableTestButton {
-  background-color: #ffc107;
-  border-color: #ffc107;
+  background-color: var(--warning-button-bg);
+  border-color: var(--warning-button-border);
+  color: var(--warning-button-text);
 }
 
 .closedDisableIssueButton {
-  background-color: #17a2b8;
-  border-color: #17a2b8;
-  color: white;
+  background-color: var(--info-button-bg);
+  border-color: var(--info-button-border);
+  color: var(--info-button-text);
 }