homebrew-bundle: `brew bundle exec` behaves unexpectedly

I have tried using brew bundle exec, but it behaves differently than I would expect. I have created a simple Brewfile that declares only Python 3.8. I expect that when I run brew bundle exec, the python3 command will point to Python 3.8. This does not seem to be the case, however – Python 3.11, which is installed globally through Brew, gets picked up instead.

~/test
❯ ls
Brewfile

~/test 
❯ cat Brewfile
tap "homebrew/bundle"
tap "homebrew/core"
brew "python@3.8"

~/test 
❯ python3 --version
Python 3.11.3

~/test 
❯ brew bundle --file=Brewfile exec -- python3 --version
Python 3.11.3

brew doctor shows no errors and brew update says everything is up to date. My OS is Pop!_OS 22.04 LTS, which is based on Ubuntu 22.04 LTS.

~/test 
❯ brew config
HOMEBREW_VERSION: 4.0.16
ORIGIN: https://github.com/Homebrew/brew
HEAD: 01e0c20d01c6aab28d844280d130f0e745e2ddd9
Last commit: 4 days ago
Core tap JSON: 04 May 18:12 UTC
HOMEBREW_PREFIX: /home/linuxbrew/.linuxbrew
HOMEBREW_CASK_OPTS: []
HOMEBREW_DISPLAY: :1
HOMEBREW_MAKE_JOBS: 12
Homebrew Ruby: 2.6.10 => /home/linuxbrew/.linuxbrew/Homebrew/Library/Homebrew/vendor/portable-ruby/2.6.10_1/bin/ruby
CPU: dodeca-core 64-bit zen
Clang: N/A
Git: 2.34.1 => /bin/git
Curl: 7.81.0 => /bin/curl
Kernel: Linux 6.2.6-76060206-generic x86_64 GNU/Linux
OS: Pop!_OS 22.04 LTS (jammy)
Host glibc: 2.35
/usr/bin/gcc: 11.3.0
/usr/bin/ruby: N/A
glibc: N/A
gcc@11: N/A
gcc: N/A
xorg: N/A