Fix bug in nuget license detection

Reference: #3409
Signed-off-by: Ayan Sinha Mahapatra <[email protected]>

Author: AyanSinhaMahapatra

src/licensedcode/data/rules/unknown-license-reference_382.RULE

@@ -0,0 +1,9 @@
+---
+license_expression: unknown-license-reference
+is_license_tag: yes
+minimum_coverage: 100
+referenced_filenames:
+    - COPYING.txt
+---
+
+<license type="file">COPYING.txt</license>

src/licensedcode/data/rules/unknown-license-reference_383.RULE

@@ -0,0 +1,9 @@
+---
+license_expression: unknown-license-reference
+is_license_reference: yes
+minimum_coverage: 100
+referenced_filenames:
+    - COPYING.txt
+---
+
+license COPYING.txt

src/licensedcode/data/rules/unknown-license-reference_384.RULE

@@ -0,0 +1,9 @@
+---
+license_expression: unknown-license-reference
+is_license_reference: yes
+minimum_coverage: 100
+referenced_filenames:
+    - COPYING.txt
+---
+
+license @type file #text COPYING.txt