[Bug fix] Fix vertex ai integration issue

[deshraj]

Description

Reported by a user on our slack here: https://embedchain.slack.com/archives/C05RG7CJKC6/p1707888213859569

Type of change

• Bug fix (non-breaking change which fixes an issue)

How Has This Been Tested?

• Unit Test

[codecov]

Codecov Report

Attention: 5 lines in your changes are missing coverage. Please review.

Comparison is base (41bd258) 56.68% compared to head (8a14edb) 56.56%.
Report is 1 commits behind head on main.

Files	Patch %	Lines
embedchain/llm/vertex_ai.py	28.57%	5 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1257      +/-   ##
==========================================
- Coverage   56.68%   56.56%   -0.13%     
==========================================
  Files         146      146              
  Lines        5943     5944       +1     
==========================================
- Hits         3369     3362       -7     
- Misses       2574     2582       +8     

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