Fix workload update API by using background context for async operation

[amirejaz]

Problem

The updateWorkload endpoint was using the HTTP request context (r.Context()) for async operations. When the handler returns, the request context gets cancelled, which can cause failures in async operations like lock acquisition.

Solution

Changed updateWorkload to use context.Background() instead of the request context, matching the pattern used by deleteWorkload, restartWorkload, and stopWorkload endpoints.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 64.20%. Comparing base (73d4f26) to head (2865162).

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3307      +/-   ##
==========================================
+ Coverage   64.18%   64.20%   +0.01%     
==========================================
  Files         365      365              
  Lines       35244    35244              
==========================================
+ Hits        22623    22629       +6     
+ Misses      10810    10803       -7     
- Partials     1811     1812       +1     

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