New thermal camera integration test failure for Edifice

After forward porting some changes from `ign-rendering4` to `main`, a new integration test failure appeared for the thermal camera. More information can be found in #246.

## Environment
* OS Version: MacOS
* Source build (commit https://github.com/ignitionrobotics/ign-rendering/commit/52c4ab0d5a57a793d90171cbc54f324e8aac37d4, `main` branch at the time of this writing)

## Description
* Expected behavior: `test/integration/thermal_camera` should pass on MacOS.
* Actual behavior: `test/integration/thermal_camera` failed on MacOS.
* `test/integration/thermal_camera` does not fail for MacOS on the `ign-rendering4` branch: https://github.com/ignitionrobotics/ign-rendering/pull/246#issuecomment-778477528

## Steps to reproduce

1. Clone the repo: `git clone https://github.com/ignitionrobotics/ign-rendering.git`
2. Complete the build so that tests are available:
```
cd ign-rendering
mkdir build
cd build
cmake ..
make
```
3. Run the thermal camera integration test:
```
# the following steps assume you are already in the ign-rendering/build directory
cd bin
./INTEGRATION_thermal_camera
```

## Output

Here is the original failure from CI in #246:
```
/Users/jenkins/workspace/ignition_rendering-ci-pr_any-homebrew-amd64/ign-rendering/test/integration/thermal_camera.cc:233
The difference between boxTemp and temp is 14, which exceeds boxTempRange, where
boxTemp evaluates to 310,
temp evaluates to 296, and
boxTempRange evaluates to 3.
```