docs: missing comma in 'Signals' codeblock

[hector97i]

Description

Added missing comma

Related Issue

#1133

Motivation and Context

How Has This Been Tested?

Screenshots (if appropriate):

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• I have run the pre-commit run command to format and lint.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have read the CONTRIBUTING document.
• I have added tests to cover my changes.
• I have added my name and/or github handle to AUTHORS.rst
• I have added my change to CHANGES.rst
• All new and existing tests passed.

[codecov]

Codecov Report

Merging #1132 (035b666) into master (4790591) will increase coverage by 0.07%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #1132      +/-   ##
==========================================
+ Coverage   97.22%   97.30%   +0.07%     
==========================================
  Files          23       23              
  Lines        1263     1263              
  Branches      205      205              
==========================================
+ Hits         1228     1229       +1     
  Misses         16       16              
+ Partials       19       18       -1     

see 1 file with indirect coverage changes

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[ddabble]

Looks good, thanks!