fix: Don't attempt rename if old DocType doesn't exist

[adityahase]

Ref: https://frappecloud.com/app/agent-job/cab67ab0d4

[codecov]

Codecov Report

Patch and project coverage have no change.

Comparison is base (acc3fa2) 2.74% compared to head (bb154a1) 2.74%.
Report is 4 commits behind head on main.

Additional details and impacted files

@@          Coverage Diff          @@
##            main   #1534   +/-   ##
=====================================
  Coverage   2.74%   2.74%           
=====================================
  Files         56      56           
  Lines       1637    1637           
=====================================
  Hits          45      45           
  Misses      1592    1592           

Files Changed	Coverage Δ
...vice_level_agreement/hd_service_level_agreement.py	0.00% <0.00%> (ø)

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