fix(make): ensure venv.execute succeeds on re-runs by resetting venv permissions

[xgantan]

Since Python 3.13, python3 -m venv can create read-only files, causing subsequent runs to fail. Pre-set write permissions on existing venv dir before recreating.

Before

$ make packer.init
make venv.execute COMMAND='cd packer/linux && packer init .'
make[1]: Entering directory '/.../agent-aws-stack'
python3 -m venv venv && \
. venv/bin/activate && \
pip install --upgrade pip && \
pip install -r requirements.txt && \
cd packer/linux && packer init . && \
deactivate && \
cd -
Error: [Errno 13] Permission denied: '/.../agent-aws-stack/venv/bin/activate.csh'
make[1]: *** [Makefile:60: venv.execute] Error 1
make[1]: Leaving directory '/.../agent-aws-stack'
make: *** [Makefile:130: packer.init] Error 2

After

$ make packer.init
make venv.execute COMMAND='cd packer/linux && packer init .'
make[1]: Entering directory '/home/xg/Workspaces/agent-aws-stack'
[ -d venv ] && chmod -R u+w venv || true && \
python3 -m venv venv && \
. venv/bin/activate && \
pip install --upgrade pip && \
pip install -r requirements.txt && \
cd packer/linux && packer init . && \
deactivate && \
cd -
...
Requirement already satisfied: pycparser in ./venv/lib/python3.13/site-packages (from cffi>=2.0.0->cryptography->ansible-core~=2.15.5->ansible==8.5.0->-r requirements.txt (line 1)) (3.0)
/.../agent-aws-stack
make[1]: Leaving directory '/.../agent-aws-stack'