Spacebar to pan across the canvas triggers constant tool changes
#### Summary:
Holding Spacebar to pan also triggers switching between selector and last selected tool
#### Steps to reproduce:
<!-- Describe what you did (step-by-step) so we can reproduce: -->
- open Inkscape
- Select any tool (eg. Bezier tool)
- Hold spacebar and move the cursor
#### What happened?
Tool kept switching between selector and Bezier tool (in the above example) during the course of panning. If the second step (selecting a tool) is ignored, the selector preferences window opens once spacebar is released.
#### What should have happened?
Panning across the canvas.
#### Debug info
```
Inkscape 1.2-dev (6dc17b5, 2021-06-05)
GLib version: 2.68.2
GTK version: 3.24.29
glibmm version: 2.66.1
gtkmm version: 3.24.5
libxml2 version: 2.9.12
libxslt version: 1.1.34
Cairo version: 1.17.4
Pango version: 1.48.5
HarfBuzz version: 2.8.1
OS version: Windows 10 1903
```
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issue