[font] Fix failure with bitmap fonts

[clydebarrow]

What does this implement/fix?

Using bitmap fonts with an array of glyphs silently fails to render anything.

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)
• Code quality improvements to existing code or addition of tests
• Other

Related issue or feature (if applicable):

• fixes Specifying (any) glyphs for a bitmap font leads to empty PROGMEM (due to EStr vs str) issues#6371

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

• esphome/esphome-docs#

Test Environment

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

Example entry for config.yaml:

# Example config.yaml
  - file: MatrixChunky8X.bdf
    glyphs:
      - T
      - e
      - x
      - t
    id: chunky

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 @esphome/core, mind taking a look at this pull request as it has been labeled with an integration (font) 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 53.98%. Comparing base (4d8b5ed) to head (ae97ec6).
Report is 1537 commits behind head on dev.

Additional details and impacted files

@@            Coverage Diff             @@
##              dev    #7691      +/-   ##
==========================================
+ Coverage   53.70%   53.98%   +0.27%     
==========================================
  Files          50       50              
  Lines        9408     9764     +356     
  Branches     1654     1344     -310     
==========================================
+ Hits         5053     5271     +218     
- Misses       4056     4167     +111     
- Partials      299      326      +27     

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