Add the webview package as git submodule instead of adding it via unity package manager.

.gitmodules

 [submodule "Assets/Plugins/JsonSubTypes"]
 	path = Assets/Plugins/JsonSubTypes
 	url = https://github.com/manuc66/JsonSubTypes
+[submodule "Packages/bessw.unity.webview"]
+	path = Packages/bessw.unity.webview
+	url = https://gl.kwarc.info/FrameIT/unity-webview.git

bessw.unity.webview @ c49f768b

+Subproject commit c49f768b41a3caf0541fcdbfa0d65b74c7e63a4f

Packages/manifest.json

 {
   "dependencies": {
-    "bessw.unity.webview": "https://gl.kwarc.info/FrameIT/unity-webview.git",
     "com.github-glitchenzo.nugetforunity": "https://github.com/GlitchEnzo/NuGetForUnity.git?path=/src/NuGetForUnity",
     "com.unity.2d.sprite": "1.0.0",
     "com.unity.2d.tilemap": "1.0.0",

Packages/packages-lock.json

 {
   "dependencies": {
     "bessw.unity.webview": {
-      "version": "https://gl.kwarc.info/FrameIT/unity-webview.git",
+      "version": "file:bessw.unity.webview",
       "depth": 0,
-      "source": "git",
-      "dependencies": {},
-      "hash": "7d6373282087b3434bc6e25a82ee2074b673ac5b"
+      "source": "embedded",
+      "dependencies": {}
     },
     "com.github-glitchenzo.nugetforunity": {
       "version": "https://github.com/GlitchEnzo/NuGetForUnity.git?path=/src/NuGetForUnity",