Improve temperature precision in BME280 and BMP280

[jxl77]

What does this implement/fix?

The RMS precision in the BME280 and BMP280 sensors is 0.002°C . But the existing routines truncated the precision to 0.01°C.
This is a very minor change that brings back the full precision to BME280 and BMP280.

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
sensor:
  - platform: bme280_i2c
    temperature:
      name: "BME280 Temperature"
      oversampling: 16x
      accuracy_decimals: 3
    pressure:
      name: "BME280 Pressure"
      accuracy_decimals: 2
    humidity:
      name: "BME280 Humidity"
      accuracy_decimals: 2
    address: 0x76
    update_interval: 5s

Checklist:

• The code change is tested and works locally. (tested for BME280 and BMP280)
• 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 (bme280_base) 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 ✅

Comparison is base (0cbc06a) 53.69% compared to head (c3c8fdb) 53.69%.

Additional details and impacted files

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  Files          50       50           
  Lines        9398     9398           
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  Hits         5046     5046           
  Misses       4053     4053           
  Partials      299      299           

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[kbx81]

LGTM -- tested with a BME280 I have here, as well.