refactor: inline _bs_icon

`_bs_icon` is only called in `icon`, so there is no reason for it to be a
separate function. Additionally, by moving it to `icon`, we can ensure that only
whitelisted icon names are used, reducing the chance of actual string injection
attacks.

app/general/templatetags/bs_icons.py

@@ -1,5 +1,3 @@
-import re
-
 from django import template
 from django.utils.safestring import mark_safe
 
@@ -12,20 +10,6 @@
 
 
 register = template.Library()
-icon_name_re = re.compile(r"[a-z0-9\-]+")
-
-
-def _bs_icon(name):
-    assert icon_name_re.fullmatch(name)
-    return mark_safe(f'<i aria-hidden="true" class="icon bi-{name}"></i> ')
-    # The trailing space is intentional: Since this is an inline element
-    # usually followed by text, the absence/presence of a space is significant,
-    # and usually wanted for layout. That's too hard to remember, so we always
-    # add it. Multiple spaces are equal to one. That way the exact layout of
-    # code in the templates doesn't matter. Beware of using {% spaceless %}
-    # which will negate this. A pure CSS solution escaped me thus far, since a
-    # space will take additional space in addition to a margin.
-
 
 # a mapping from project types to Bootstrap icon names:
 _icons = {
@@ -44,4 +28,14 @@ def icon(name):
     if not (bs_name := _icons.get(name)):
         raise template.TemplateSyntaxError(f"'icon' requires a registered icon name (got {name!r})")
 
-    return _bs_icon(bs_name)
+    # This `mark_safe` is okay because we only allow certain, whitelisted strings. This is enforced above by fetching it
+    # from the `_icons` dictionary
+    return mark_safe(f'<i aria-hidden="true" class="icon bi-{bs_name}"></i> ')  # noqa: S308 - see above
+
+    # The trailing space is intentional: Since this is an inline element
+    # usually followed by text, the absence/presence of a space is significant,
+    # and usually wanted for layout. That's too hard to remember, so we always
+    # add it. Multiple spaces are equal to one. That way the exact layout of
+    # code in the templates doesn't matter. Beware of using {% spaceless %}
+    # which will negate this. A pure CSS solution escaped me thus far, since a
+    # space will take additional space in addition to a margin.