Make scripts/insert-includes.py use Python from conda env

[hansungk]

This fixes CI for CVA6/nvdla on a system that does not have a /usr/bin/python interpreter by making the script use one from conda env.

Before, CI for prepare-chipyard-cores and prepare-chipyard-accel would fail on this particular system when building cva6 and nvdla that uses this script:

make[1]: /scratch/buildbot/actions-runner/_work/chipyard/chipyard/scripts/insert-includes.py: No such file or directory
/scratch/buildbot/actions-runner/_work/chipyard/chipyard/scripts/insert-includes.py combined.sv /scratch/buildbot/actions-runner/_work/chipyard/chipyard/generators/cva6/src/main/resources/cva6/vsrc/CVA6CoreBlackbox.preprocessed.sv /scratch/buildbot/actions-runner/_work/chipyard/chipyard/generators/cva6/src/main/resources/cva6/vsrc/cva6/src/fpga-support/behav/common/include /scratch/buildbot/actions-runner/_work/chipyard/chipyard/generators/cva6/src/main/resources/cva6/vsrc/cva6/src/common_cells/include /scratch/buildbot/actions-runner/_work/chipyard/chipyard/generators/cva6/src/main/resources/cva6/vsrc/cva6/src/pmp/include /scratch/buildbot/actions-runner/_work/chipyard/chipyard/generators/cva6/src/main/resources/cva6/vsrc/cva6/src/fpu/tb/flexfloat/include /scratch/buildbot/actions-runner/_work/chipyard/chipyard/generators/cva6/src/main/resources/cva6/vsrc/cva6/src/fpu/src/common_cells/include /scratch/buildbot/actions-runner/_work/chipyard/chipyard/generators/cva6/src/main/resources/cva6/vsrc/cva6/src/axi/include /scratch/buildbot/actions-runner/_work/chipyard/chipyard/generators/cva6/src/main/resources/cva6/vsrc/cva6/include 
make[1]: *** [Makefile:150: /scratch/buildbot/actions-runner/_work/chipyard/chipyard/generators/cva6/src/main/resources/cva6/vsrc/CVA6CoreBlackbox.preprocessed.sv] Error 127

Related PRs / Issues:

Type of change:

• Bug fix
• New feature
• Other enhancement

Impact:

• RTL change
• Software change (RISC-V software)
• Build system change
• Other

Contributor Checklist:

• Did you set main as the base branch?
• Is this PR's title suitable for inclusion in the changelog and have you added a changelog:<topic> label?
• Did you state the type-of-change/impact?
• Did you delete any extraneous prints/debugging code?
• Did you mark the PR with a changelog: label?
• (If applicable) Did you update the conda .conda-lock.yml file if you updated the conda requirements file?
• (If applicable) Did you add documentation for the feature?
• (If applicable) Did you add a test demonstrating the PR?

• (If applicable) Did you mark the PR as Please Backport?