fix: runtime mock support initHandler

[echosoar]

No description provided.

[gitpod-io]

[codecov-io]

Codecov Report

Merging #749 (0b4108d) into 2.x (87247ea) will decrease coverage by 0.16%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##              2.x     #749      +/-   ##
==========================================
- Coverage   86.61%   86.45%   -0.17%     
==========================================
  Files         142      144       +2     
  Lines        5814     5884      +70     
  Branches     1081     1087       +6     
==========================================
+ Hits         5036     5087      +51     
- Misses        746      765      +19     
  Partials       32       32              

Impacted Files	Coverage Δ
packages-serverless/runtime-mock/src/runtime.ts	66.12% <100.00%> (+1.12%)	⬆️
packages/bootstrap/src/bootstrap.ts	70.31% <0.00%> (ø)
packages/bootstrap/src/index.ts	100.00% <0.00%> (ø)

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