DOC: Do not use unfinished double backticks

Do not use unfinished double backticks: Sphinx interprets them as
unfinished inline literals. Change them to quotes in third-party
licence documentation.

Fixes:
```
/dipy/segment/mask.py:docstring of dipy.segment.mask.median_otsu:65:
 WARNING: Inline literal start-string without end-string.
```

and
```
/dipy/workflows/docstring_parser.py:docstring of dipy.workflows.docstring_parser:17:
 WARNING: Inline literal start-string without end-string.
```

raised for example at:
https://github.com/dipy/dipy/actions/runs/10472634043/job/29002561651#step:5:1146
and
https://github.com/dipy/dipy/actions/runs/10472634043/job/29002561651#step:5:1145

dipy/segment/mask.py

@@ -194,7 +194,7 @@ def median_otsu(
         used to endorse or promote products derived from this software without
         specific prior written permission.
 
-    THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
+    THIS SOFTWARE IS PROVIDED BY THE AUTHOR "AS IS" AND ANY EXPRESS OR
     IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
     WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
     DISCLAIMED. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT,

dipy/workflows/docstring_parser.py

@@ -15,7 +15,7 @@
     the documentation and/or other materials provided with the
     distribution.
 
-THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
+THIS SOFTWARE IS PROVIDED BY THE AUTHOR "AS IS" AND ANY EXPRESS OR
 IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
 WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
 DISCLAIMED. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT,