Fix panic in GQL batch request

[dirkkul]

What's being changed:

Adds check for casting and return error if not possible.

Closes #3258
Fixes CVE-2023-38976

Review checklist

• All new code is covered by tests where it is reasonable.

[codecov]

Codecov Report

Patch coverage has no change and project coverage change: -0.01% ⚠️

Comparison is base (0e6c9ba) 64.11% compared to head (239a81c) 64.10%.
Report is 3 commits behind head on stable/v1.21.

❗ Current head 239a81c differs from pull request most recent head 545de1b. Consider uploading reports for the commit 545de1b to get more accurate results

Additional details and impacted files

@@               Coverage Diff                @@
##           stable/v1.21    #3431      +/-   ##
================================================
- Coverage         64.11%   64.10%   -0.01%     
================================================
  Files               757      757              
  Lines             76871    76882      +11     
================================================
+ Hits              49286    49288       +2     
- Misses            24525    24532       +7     
- Partials           3060     3062       +2     

Files Changed	Coverage Δ
adapters/handlers/rest/handlers_graphql.go	0.00% <0.00%> (ø)
modules/generative-openai/config/class_settings.go	75.89% <ø> (ø)
modules/generative-palm/clients/palm.go	53.12% <ø> (-0.37%)	⬇️

... and 4 files with indirect coverage changes

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[sonarqubecloud]

Kudos, SonarCloud Quality Gate passed!   

0 Bugs
0 Vulnerabilities
0 Security Hotspots
0 Code Smells

No Coverage information
0.0% Duplication