Canon lens handling regression in 0.28.0

Describe the bug

Up to and including 0.27.7-release, I'm able to get correct lens detection for this lens setup in Darktable, by putting this in ~/.exiv2:

[canon]
748=Canon EF 100-400mm f/4.5-5.6L IS II USM + 1.4x extender

But with 0.28.0-release, that doesn't work anymore, and the lens is misdetected as Tamron. Nothing else I've tried has worked. In particular, when I tried patching out the conflicting Tamron lenses, Darktable reported "Lens 748 not found" or words to that effect, even though obviously the Canon 748 entry is still there. This is the patch I tried:

--- exiv2-0.28.0/src/canonmn_int.cpp.dist       2023-05-08 11:01:13.000000000 -0500
+++ exiv2-0.28.0/src/canonmn_int.cpp    2023-08-26 12:42:58.326572444 -0500
@@ -1865,8 +1865,6 @@ constexpr TagDetails canonCsLensType[] =
                                           {747, "Canon EF 100-400mm f/4.5-5.6L IS II USM"},
                                           {747, "Tamron SP 150-600mm f/5-6.3 Di VC USD G2"},  // 1
                                           {748, "Canon EF 100-400mm f/4.5-5.6L IS II USM + 1.4x"},
-                                          {748, "Tamron 100-400mm f/4.5-6.3 Di VC USD + 1.4x"},  // 1
-                                          {748, "Tamron 70-210mm f/4 Di VC USD + 2x"},           // 2
                                           {749, "Tamron 100-400mm f/4.5-6.3 Di VC USD + 2x"},
                                           {749, "Canon EF 100-400mm f/4.5-5.6L IS II USM + 2x"},  // 1
                                           {750, "Canon EF 35mm f/1.4L II USM"},

The most worrisome syndrome though is that the override entry in ~/.exiv2 is being ignored.

To Reproduce

I've posted a CR2 with this lens here

(github has a 25MB attachment limit, and doesn't allow CR2 files besides.)

I'm running Darktable 4.4.2 but it wasn't the variable, and it's detecting the lens correctly when built and linked against exiv2-0.27.7.

To see the syndrome, set up the ~/.exiv2 above, import the picture into DT, and admire the detected lens ID on the left.

Note that you'll see the no-lens-info error in the lens correction tool for both the Canon and Tamron versions of ID 748. I run a Lensfun with the correction data for the Canon setup patched in.

Expected behavior

In the left pane with the image attributes, the lens entry should read

Canon EF 100-400mm f/4.5-5.6L IS II USM + 1.4x extender

(Which is what it says when built+linked with v0.27.7, and it's what I have in my ~/.exiv2.)

Desktop (please complete the following information):

Gentoo
exiv2 0.27.7 vs 0.28.0
gcc-11.4.1

built out of Gentoo portage. with these use flags:

U I
- - abi_x86_32 : 32-bit (x86) libraries
+ + bmff       : Add support for the ISOBMFF format
- - doc        : Add extra documentation (API, Javadoc, etc). It is recommended to enable per package instead of globally
- - examples   : Install examples, usually source code
+ + nls        : Add Native Language Support (using gettext - GNU locale utilities)
+ + png        : Add support for libpng (PNG images)
- - test       : Enable dependencies and/or preparations necessary to run tests (usually controlled by FEATURES=test but can be toggled independently)
- - webready   : Support reading metadata over the internet
+ + xmp        : Enable support for Extensible Metadata Platform (Adobe XMP)

Additional context

I believe this DT issue relates: https://github.com/darktable-org/darktable/issues/14882

Exiv2 / exiv2