Minor improvement of docs of gallery example "Colorbars"

[yvonnefroehlich]

Description of proposed changes

For context please see #2395 (comment) and #2395 (comment).

Related to issue #2437

Reminders

• Run make format and make check to make sure the code follows the style guide.
• Add tests for new features or tests that would have caught the bug that you're fixing.
• Add new public functions/methods/classes to doc/api/index.rst.
• Write detailed docstrings for all functions/methods.
• If wrapping a new module, open a 'Wrap new GMT module' issue and submit reasonably-sized PRs.
• If adding new functionality, add an example to docstrings or tutorials.
• Use underscores (not hyphens) in names of Python files and directories.

Slash Commands

You can write slash commands (/command) in the first line of a comment to perform
specific operations. Supported slash commands are:

• /format: automatically format and lint the code
• /test-gmt-dev: run full tests on the latest GMT development version

[seisman]

I don't think the changes are accurate. For frames with non-rectangle boundaries, using jBL doesn't place the colorbar inside the frame boundary.

>>> import pygmt
>>> fig = pygmt.Figure()
>>> fig.basemap(region="g", frame=True, projection="H10c")
>>> fig.colorbar(position="jBL+w3c+h", cmap="turbo", frame=True)
>>> fig.show()

[yvonnefroehlich]

I don't think the changes are accurate. For frames with non-rectangle boundaries, using jBL doesn't place the colorbar inside the frame boundary.

That's a good point! But based on this also the old formulation "map frame" is not accurate. Maybe "bounding box" is the precise term here? Please see commit 8b463f6.