[bang-bang] Remove assert()

[kbx81]

What does this implement/fix?

Removes an assert() from bang-bang -- this doesn't need to crash the device here. Changed to print a warning and move along.

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): fixes

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

Test Environment

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

Example entry for config.yaml:

# Example config.yaml

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 @OttoWinter, mind taking a look at this pull request as it has been labeled with an integration (bang_bang) 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 54.01%. Comparing base (4d8b5ed) to head (d8ad431).
Report is 1393 commits behind head on dev.

Additional details and impacted files

@@            Coverage Diff             @@
##              dev    #7533      +/-   ##
==========================================
+ Coverage   53.70%   54.01%   +0.30%     
==========================================
  Files          50       50              
  Lines        9408     9695     +287     
  Branches     1654     1711      +57     
==========================================
+ Hits         5053     5237     +184     
- Misses       4056     4127      +71     
- Partials      299      331      +32     

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