SECURITY: Drop "patch level" from the supported version number list

This commit drops the "patch level" from the supported version numbers
listed in the security policy document because:

1. It currently does not convey any meaningful information (simply set
   to "0") and is really unnecessary because the support status is
   defined at the "minor" version level.

2. Updating the security policy document whenever there is a new "patch
   release" is arguably too noisy and does not add much value.

Signed-off-by: Stephanos Ioannidis <stephanos.ioannidis@nordicsemi.no>

.github/SECURITY.md

@@ -8,12 +8,12 @@ updates:
   - The most recent release, and the release prior to that.
   - Active LTS releases.
 
-At this time, with the latest release of v3.3.0, the supported
+At this time, with the latest release of v3.3, the supported
 versions are:
 
-  - v2.7.0: Current LTS
-  - v3.2.0: Prior release
-  - v3.3.0: Current release
+  - v2.7: Current LTS
+  - v3.2: Prior release
+  - v3.3: Current release
 
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