Remove extra bottom padding in InfoCard content

Fixes #5396 by overriding padding-bottom to undefined for MuiCardContent
in rootTheme.ts.

Signed-off-by: Mike Lewis <mtlewis@users.noreply.github.com>

.changeset/khaki-singers-perform.md

@@ -0,0 +1,5 @@
+---
+'@backstage/theme': patch
+---
+
+Remove extra bottom padding in InfoCard content

packages/theme/src/baseTheme.ts

@@ -257,6 +257,9 @@ export function createThemeOverrides(theme: BackstageTheme): Overrides {
         // etc) end up at the bottom of the card instead of just below the body
         // contents.
         flexGrow: 1,
+        '&:last-child': {
+          paddingBottom: undefined,
+        },
       },
     },
     MuiCardActions: {