Fix Nextion set_component_picture call

[edwardtfn]

What does this implement/fix?

This fixes the call to the Nextion display to change the pic id from a component. It was previously changing the attribute val, which is related to something else. In addition, I've changed the parameter for picture_id to be uint_8, as Nextion requires an integer from 0 to 255 on this attribute.

Types of changes

• Bugfix (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 not work as expected)
• Other

Related issue or feature (if applicable): N/A

Pull request in esphome-docs with documentation (if applicable): N/A

Test Environment

• ESP32
• ESP32 IDF
• ESP8266
• RP2040
• BK72xx
• RTL87xx

Example entry for config.yaml:

N/A

API inline doc updated.

Checklist:

• The code change is tested and works locally.
• Tests have been added to verify that the new code works (under tests/ folder).

If user exposed functionality or configuration variables are added/changed:

• Documentation added/updated in esphome-docs.

[probot-esphome]

Hey there @SenexCrenshaw, mind taking a look at this pull request as it has been labeled with an integration (nextion) you are listed as a code owner for? Thanks!
_{^{(message by CodeOwnersMention)}}

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 53.50%. Comparing base (4d8b5ed) to head (6dc84f7).
Report is 206 commits behind head on dev.

Additional details and impacted files

@@            Coverage Diff             @@
##              dev    #6378      +/-   ##
==========================================
- Coverage   53.70%   53.50%   -0.20%     
==========================================
  Files          50       50              
  Lines        9408     9516     +108     
  Branches     1654     1683      +29     
==========================================
+ Hits         5053     5092      +39     
- Misses       4056     4117      +61     
- Partials      299      307       +8     

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[kbx81]

LGTM -- thanks!