Bump scipp from 25.5.1 to 25.8.0 in /requirements

Bumps [scipp](https://github.com/scipp/scipp) from 25.5.1 to 25.8.0.
- [Release notes](https://github.com/scipp/scipp/releases)
- [Commits](scipp/scipp@25.05.1...25.08.0)

---
updated-dependencies:
- dependency-name: scipp
  dependency-version: 25.8.0
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

Signed-off-by: dependabot[bot] <[email protected]>

Author: dependabot[bot]

requirements/base.txt

@@ -68,7 +68,7 @@ python-dateutil==2.9.0.post0
     #   scippnexus
 sciline==25.5.2
     # via -r base.in
-scipp==25.5.1
+scipp==25.8.0
     # via
     #   -r base.in
     #   scippneutron

requirements/basetest.txt

@@ -19,10 +19,6 @@ cycler==0.12.1
     # via matplotlib
 decorator==5.2.1
     # via ipython
-exceptiongroup==1.3.0
-    # via
-    #   ipython
-    #   pytest
 executing==2.2.0
     # via stack-data
 fonttools==4.59.0
@@ -98,7 +94,7 @@ python-dateutil==2.9.0.post0
     # via matplotlib
 requests==2.32.4
     # via pooch
-scipp==25.5.1
+scipp==25.8.0
     # via tof
 scipy==1.15.3
     # via
@@ -110,18 +106,14 @@ stack-data==0.6.3
     # via ipython
 tof==25.5.0
     # via -r basetest.in
-tomli==2.2.1
-    # via pytest
 traitlets==5.14.3
     # via
     #   comm
     #   ipython
     #   ipywidgets
     #   matplotlib-inline
 typing-extensions==4.14.1
-    # via
-    #   exceptiongroup
-    #   ipython
+    # via ipython
 urllib3==2.5.0
     # via requests
 wcwidth==0.2.13